Kate Warne was an American law enforcement officer best known as the first female detective in the United States, for the Pinkerton National Detective Agency. She also had a role in uncovering the 1861 Baltimore Plot against President-elect Abraham Lincoln, recruiting female agents for the Pinkerton Agency, and conducting intelligence work for the Union during the American Civil War.

Pinkerton is a private security guard and detective agency established around 1850 in the United States by Scottish-born American cooper Allan Pinkerton and Chicago attorney Edward Rucker as the North-Western Police Agency, which later became Pinkerton & Co. and finally the Pinkerton National Detective Agency. At the height of its power from the 1870s to the 1890s, it was the largest private law enforcement organization in the world. It is currently a subsidiary of Swedish-based Securitas AB.