Colusa County was established in 1850 as one of the original 27 counties created by the first state legislature. It once encompassed all of what is now Glenn County and a portion of Tehama County. In 1891, the counties of Glenn and Colusa were split. Records prior to 1891 are still maintained in Colusa County, and those pertaining to Glenn County after the split can be found at the Glenn County recorder’s office.