California Code, Education Code - EDC § 18021

The State Librarian shall determine and certify, on or before June 1, 1982, and June 1 of each fiscal year thereafter, the population served by each public library of the state based upon census data compiled by the United States Department of Commerce or estimates prepared by the California Department of Finance, whichever is more current.  For such purposes, no person shall be deemed to be served by more than one public library.