The Colusa County Courthouse has been in continuous service since March 1, 1861 and is the present site of most county governmental offices.The tower and bell were added to the building in 1886. It is the second oldest working courthouse in California (Mariposa, the oldest). It was designed by Marysville (California) architect, Vincent Brown and constructed by James Plummer. It is located in the City of Colusa, the county seat. The movie "To Kill A Mockingbird", was filmed at this location.