California Code, Health and Safety Code - HSC § 40520

Upon adoption of its budget for the next fiscal year, the south coast district board shall apportion the amount that each county included within the south coast district shall pay to finance the operation of the south coast district in that fiscal year.

The apportionment to a county shall, as determined by the south coast district board, be that proportion of the amount that the population of the portion of the county included within the south coast district bears to the total population of the south coast district, either as determined from the latest federal decennial census or as determined from the latest annual population estimate by the Department of Finance made pursuant to subdivision (g) of Section 13073.5 of the Government Code.