Described by Allan Pinkerton as a slender, brown haired woman, there is not much else known about Kate Warne prior to when she walked into the Pinkerton Detective Agency in 1856. Born in New York, Warne became a widow shortly after she married. Kate Warne was left as a young childless widow in search of work. In answer to an ad in a local newspaper, Kate Warne walked into Allan Pinkerton’s Chicago office in search of a job. There is still debate whether or not she walked in with intentions to become a detective or just a secretary. Women were not detectives until well after the Civil War. Allan Pinkerton himself claimed that Kate Warne came into his agency and demanded to become a detective. According to Pinkerton's records, he
"was surprised to learn Kate was not looking for clerical work, but was actually answering an advertisement for detectives he had placed in a Chicago newspaper. At the time, such a concept was almost unheard of. Pinkerton said " It is not the custom to employ women detectives!" Kate argued her point of view eloquently - pointing out that women could be "most useful in worming out secrets in many places which would be impossible for a male detective." A Woman would be able to befriend the wives and girlfriends of suspected criminals and gain their confidence. Men become braggarts when they are around women who encourage them to boast. Kate also noted, Women have an eye for detail and are excellent observers."
Warne's arguments swayed Pinkerton, who at 10 o'clock on the morning of August 23, 1856 employed Kate Warne as the first female detective . Pinkerton soon had a chance to put Kate to the test. Would, as Kate had insisted, her gender allow Kate to infiltrate social situations that would bring clues to light? In 1858 Kate was involved in the case of Adams Express Company embezzlements where she was successfully able to bring herself into the confidence of the wife of the prime suspect, Mr. Maroney. She thereby acquired the valuable evidence leading to the husbands conviction. Mr. Maroney was an expressman living in Montgomery, Alabama. The Maroney’s stole $50,000 from the Adams Express Company. With Warne’s help, $39,515 was returned. Mr. Maroney was convicted and sentenced to ten years in Montgomery, Alabama. See further details about the Adams Express Company Case against Mr. Maroney.
Pre Civil War- "The Baltimore Plot" of 1861
Allan Pinkerton was secured by Samuel H. Felton, president of the Philadelphia, Wilmington and Baltimore Railroad, to investigate secessionist activity in Maryland. Felton believed that threats of damage to the railroad by "roughs and secessionists of Maryland." Allan Pinkerton soon was at work, placing agents at various points in Maryland to investigate the possibility of damage to the railroad. As the information came forth, Pinkerton became increasingly aware that the activity in Maryland did not just end with the railroad, but included the president-elect, Abraham Lincoln. Pinkerton received permission to continue his investigation and focus on the possible assassination plot.
As part of Allan Pinkerton's team at the Pinkerton National Detective Agency, Kate was one of five agents sent to Baltimore, Maryland on February 3, 1861 to investigate the hotbed of secessionist activity occurring just months prior to the inauguration of Abraham Lincoln.  (see also Maryland in the Civil War .) During the investigation, evidence supported attacks on the railroads and also unveiled the plot to assassinate president-elect Abraham Lincoln on his way to take office. The secessionist feeling in Baltimore was that if Lincoln came through the city that he would leave in a casket. Under the aliases Mrs. Cherry and Mrs. M. Barley (M.B.) Kate tracked suspicious movement among the Baltimore secessionist  It was in part through her undercover work in the guise of
a rich southern lady visiting Baltimore with a thick southern accent that apparently Mrs. Warne infiltrated secessionist social gatherings in the Baltimore area, places such as the classy Barnum Hotel posing as a flirting "southern bell" and was quick to not only verify that there was a plot to assassinate Lincoln, she developed details of how the assassination was going to occur. 
Pinkerton had agents across Maryland and details kept unraveling. However, it was Kate specifically who supplied many key details to Allan Pinkerton and Pinkerton believed the plot was eminent. Warne had befriended secessionist in Maryland and collected many details in the plot to assassinate Abraham Lincoln.
The President-elect, Abraham Lincoln was traveling from his home Springfield, Illinois to the capital via a train tour that was to stop at notable cities along the way. His published program showed that Lincoln's last leg of the journey was from Harrisburg, Pennsylvania to Washington, D.C. Due to the configuration of the trains system, all southbound trains required a transfer to be made in Baltimore, Maryland. The Northbound station ended at Calvert Street and the Southbound train station started at Camden Street (now the Camden Yards station.) The distance between these two stations were about a mile by carriage ride. The secessionist plot to kill Lincoln was
just as Mr. Lincoln would be passing through the narrow vestibule of the Depot at Calvert St. Station, to enter his carriage. A row or fight was to be got up by some outsiders to quell which the few policemen at the Depot would rush out, thus leaving Mr. Lincoln entirely unprotected and at the mercy of a mob of Secessionists who were to surround him at that time. A small Steamer had been chartered and was lying in one of the Bays or little streams running into the Chesapeake Bay, to which the murderers were to flee and it was immediately to put off for Virginia.
After seeing the pieces of the plot coming together, Pinkerton requested of Kate on the morning of February, 18th to take the 5:10 evening train to New York City. Once there, she was to set up a meeting with Norman B. Judd and place into his confidence a letter from Pinkerton stating all of the hereto discovered details of the assassination attempt. After Kate Warne supplied details of The Baltimore Plot to Norman Judd, Judd set up a meeting between himself, Allan Pinkerton and Abraham Lincoln on the 21st of February.  At this meeting, Lincoln was doubtful about an assassination plot, or that if such a plot existed that it should be taken seriously. However, a second independent source confirmed the plot by way of Frederick W. Seward, son of William H. Seward (the secretary of state designate.)  From this point, Lincoln agreed that the assassination plot was plausible enough to take action. Lincoln decided to avoid hazard where it was not necessary, however he refused to cancel any of his scheduled plans in Harrisburg. His agenda included giving three speeches, raising of the American flag at Independence Hall and attending a high profile dinner. Accordingly, they made train arrangements that allowed Lincoln to fulfill his scheduled duties in Harrisburg. It wasn't until 5:45 that night that there was any deviation from his schedule. John George Nicolay, Lincoln's private secretary interrupted the dinner party to excuse the president-elect. Lincoln then changed into a traveling suit, a soft felt cap and carried a shawl upon one arm to play the role of an invalid. Pinkerton meanwhile had the telegraph lines interrupted to prevent any knowledge of the deviation in the president-elect's schedule. At the station, Kate Warne entered the sleeping car through the rear along with Allan Pinkerton, Ward Hill Lamon and a still disguised Abraham Lincoln. She greeted president-elect Lincoln loudly as she would have a true brother. From Harrisburg, Lincoln rode to Philadelphia by a special Pennsylvania Railroad train. From Philadelphia he went to Baltimore by a special Philadelphia, Wilmington, and Baltimore train on the night of February 22/23. It is said that Warne did not sleep a wink on the overnight trip from Pennsylvania to Washington D.C that stopped in Baltimore. The disguises provided by Warne that night enabled Lincoln to make it through Baltimore without recognition and take his seat in the White House. It is believed that Pinkerton came up with the slogan to his agency "we never sleep" as a result of Kate Warne's guard of Lincoln that night. Kate was a key player in the foiled Baltimore assassination plot. Not only did she help to uncover details of the planned plot, but she also carried out most of the arrangements to smuggle Lincoln into Washington DC under secret cover. She couriered secret information and set up meetings as well as securing the necessary four berths on a train leaving Philadelphia under the pretext that these births were for her sick brother and family members. The train pulled out shortly before 11 p.m. and arrived in Baltimore about 3:30 a.m. on February 23. Kate remained in Baltimore as the sleeping cars with Lincoln on board were shifted to another train, which arrived in Washington around 6 a.m.
Civil War- "Intelligence Work for the Union" April 1861-1865
During the Civil War, Allan Pinkerton and Kate Warne were used as a covert war intelligence-gathering bureau. She could easily penetrate into southern social gatherings. Warne said that women are most useful in worming out secrets in many places which would be impossible for a male detective. Believed to be a mistress of Allan Pinkerton, the two would often pose as a married couple while undercover. She also had an assortment of names: Kay Warne, Kay Waren, Kay Warren, Kate Warne, Kate Waren, Kate Warren, Kitty Warne, Kitty Waren, Kitty Warren, Kittie Waren, Kittie Warne, and Kittie Warren. Warne was known as Kitty to Robert Pinkerton, Allan's brother. Robert Pinkerton often argued with Kate Warne over expenses turned over to the agency, but her relationship with Allan remained for years. After the quelled assassination attempt on Abraham Lincoln, Kate continued to travel with Allan Pinkerton as his Female Superintendent of Detectives. On April 12, 1861 the Confederate States of America's cannons in Charleston began firing on Fort Sumter. These cannon shells marked the beginning of the Civil War. Within nine days, Pinkerton wrote to the now President, Lincoln, offering the services of the Pinkerton National Detective Agency. However, before Lincoln could respond, Major General George B. McClellan asked Pinkerton to set up a military intelligence service for McClellan's command. Therefore, by the end of July, 1861 Pinkerton took Kate, Timothy Webster and later George Bangs west to set up a headquarters in Cincinnati, Ohio (see also Cincinnati in the Civil War) to follow McClellan's Ohio division.
Post Civil War- "Continued Espionage" 1865-1867
After successfully delivering the president elect to the White House, Kate worked on various high profile cases. One of which involved the murder of a bank-teller, George Gordon, in Atkinson, Mississippi. The murderer got away with $130,000.00. Pinkerton determined that George Gordon was fetching money for a friend or someone who frequented the bank, but was then stuck initially on the head behind the ear with a hammer with intent to murder any witnesses of the robbery. Through his investigation, Pinkerton felt certain that his prime suspect, Alexander P. Drysdale had in fact killed Gordon. However, at this point he did not have enough hard evidence to convict Drysdale... too much was still based on speculation. Therefore, he set a trap for Drysdale ala Shakespeare's "Hamlet" so that he would reveal a confession. Kate Warne was sent under cover as a Mrs. Potter and became close friends with Mr. Drysdale's wife. Through this plot, they were able to uncover where Drysdale had hidden the stolen money.
Another case that Kate went undercover for, was that brought about by a Captain Sumner who was convinced that both his sister, Mrs. Annie Thayer and Mr.Pattmore were attempting to poision Mrs. Pattmore and himself. Warne took the name Lucille and took on the role of a pseudo-fortune teller to lure information out of the suspected murderer's confidants. In the meantime, she also continually coordinated Pinkerton's other female detectives in the agency. Pinkerton rented a space for Warne to work as part of her guise.
Allan Pinkerton named Kate Warne one of the five best detectives that he had. Her convincing Pinkerton to employ her was a significant moment in woman's history. Women were not allowed to be a part of the police force until 1891 and could not be detectives until 1903.
This photo comes from the Library of Congress. Seated R. William Moore and Allan Pinkerton (right); standing: George H. Bangs, John C. Babcock, and Augustus K. Littlefield.
Allan Pinkerton specifically thanks two people in his memoirs; Kate Warne and Timothy Webster, a detective that is executed during the Civil War for espionage. Both Warne and Webster were key operatives during the Baltimore Plot investigations. Kate Warne reported back to Pinkerton about all her work when he was away from the office and they worked together on numerous cases during their tenure. Pinkerton constantly showed a deep trust in the work that Warne performed and acknowledges so in his memoirs. She was in charge of the Female Detective Bureau, established by Allan Pinkerton. Her title was Supervisor of Women Agents. Allan Pinkerton said to his female prospective agents:
“In my service you will serve your country better than on the field. I have several female operatives. If you agree to come aboard you will go in training with the head of my female detectives, Kate Warne. She has never let me down (Rinaldi 133).”
Kate Warne did not survive long after the Civil War. She suddenly caught pneumonia on New Year's Day, 1868, and died on the 28th with Pinkerton at her bedside. She's buried in the Pinkerton Family Plot in Chicago Illinois' Graceland Cemetery. The grave is marked in the Graceland Cemetery under the name of Kate Warn and that she died of congestion of the lungs at the age of 38. She was buried January 30, 1868.
- Blood on the Moon: the Assassination of Abraham Lincoln by Edward Steers 2005
- Girl in Blue by Ann Rinaldi 2001
- The Enemy Within:The History of Espionage by Terry Cowdy 2006
- Spy on the Rebellion by Allan Pinkerton 1883
- The Murderer and the Fortune Teller by Allan Pinkerton 1877
- The Complete Idiot's Guide to the Civil War, 2nd Edition by Alan Axelrod 2003
- Herndon's Informants: Letters, Interviews and Statements about Abraham Lincoln Edited by Douglas L. Wilson and Rodney O. Davis 1998
- Historical Dictionary of the Civil War and Reconstruction By William L. Richter 2004
- Intelligence in the Civil War by CIA Office of Public Affairs 2007
- The Hoofs and Guns of the Storm: Chicago's Civil War Connections By Arnie Bernstein 2003
- Wild Train: The Story of the Andrews Raiders By Charles O'Neill 1956
- Come Retribution: The Confederate Secret Service and the Assassination of Abraham Lincoln By William A. Tidwell, James O. Hall, David Winfred Gaddy 1988
- Call in Pinkerton's: American Detectives at Work for Canada By David Ricardo Williams 1998
- Pinkerton Government Services Inc. Pinkerton Government Services Inc. 2006
- Answers.com Answers Corporation 2007
- Crimelibrary.com Turner Entertainment 2007
- PI Mall Thomas Investigative Publications 2007
- SameShield SameShield 2007
- Final Report of the Select Committee to Study Governmental Operations with Respect to Intelligence Activities U.S Senate 1976