The county was created by the Colorado leglislature on April 15, 1901, out of Arapahoe County. Portions were taken away in 1903 for Washington and Yuma counties, and 53 square miles were transferred to the City and County of Denver in 1989 to provide land for Denver International Airport. Adams lost additional territory in its northwest corner on November 15, 2001, when the City and County of Broomfield were created.
Source: wikipedia.org