The Knox County Courthouse, located on the public square of Knoxville near its associated hall of records, is the former county courthouse of Knox County, Illinois. The courthouse was built in 1840 to replace the county's first courthouse; built in 1831 shortly after the county's organization, it had been outgrown by the end of the decade. Architect John Mandeville gave the building its Greek Revival design. The Hall of Records, which was designed by Charles Ulricson, was added in 1854 to house county records after the courthouse ran out of space for them. The Knox County seat moved to Galesburg in 1873; the courthouse and hall of records subsequently housed the Knoxville city hall and public library respectively until 1978, when the city government moved to the hall and the courthouse became a museum.