 A courthouse was built in Watseka in 1866 at a cost of $28,000 and included a jail in the basement; this building was expanded in 1881, and a new jail was built in 1893 just east of the courthouse.According to the U.S. Census Bureau, the county has a total area of , of which is land and (0.1%) is water.It is the third-largest county in Illinois by land area and the fifth-largest by total area.