Size of Business Data for California (Quarterly)
These tables are from "California Size of Business – – Number of Businesses by Employment Size, and Industry" for 2010 - 2019.
For a explanation of what industries are included.
Additional size of business data by county and industry are available from the U.S. Census Bureau in their "County Business Patterns" report. The data for 1998 to the present are available by NAICS and 1994 to 1997 by Standard Industry Classification.