California Code, Government Code - GOV § 24256

Whenever the law specifies that an office or building shall be located at the county seat and an incorporated city has been designated as the county seat, the location of that office or building may be either within or in the immediate vicinity of the corporate limits of said city.  However, the prescribed offices and buildings may be situated outside the county seat or its immediate vicinity, provided that those offices and buildings are conveniently located and easily accessible to the public, and notice of their location is prominently displayed in the county administration building and other appropriate county facilities.