California Code, Government Code - GOV § 24254.5

Sheriffs and clerks shall also have offices in each city wherein the city hall is not less than eighteen miles from the site of the county courthouse and which has a population of not less than ten thousand, and within the ten-mile radius from the city hall of which there is a population of not less than fifty thousand, if there are residing in the county at least eighteen miles from the county courthouse not less than fifteen thousand persons, some of whom would be required to travel 50 miles to attend court at said city and at least ten miles farther in order to attend the superior court at the county courthouse, and in each city or town within the county containing a population of not less than two thousand two hundred wherein the city hall of said city or town is not less than sixty miles distant from the site of the county courthouse, or any other place where sessions of the superior court have been established, such populations being ascertained by the latest population determination as made under the authority of the Congress of the United States, or the Legislature of the State of California.