Estimating Unauthorized Immigrant Populations in Sub-State Areas: California as a Test Case

Laura Hill, Public Policy Institute of California (PPIC)
Hans Johnson, Public Policy Institute of California (PPIC)

California is home to approximately 2.6 million unauthorized immigrants. Careful estimates at the state level are published regularly, but do not provide information about the distribution of the population within the state. We propose to develop the first-ever estimates of the unauthorized immigrant population for California’s counties and some sub-county areas. We will use several datasets, relying primarily on newly generated and recently available data derived from IRS tax filings. Since 1996, unauthorized immigrants have been able to file tax returns using Individual Taxpayer Identification Numbers (ITINs) on their 1040 forms. The IRS has made counts of ITIN filers for each zip code publicly available for tax years 2000-2007. California is the state for which ITINs are most likely to be reliable predictor of the unauthorized immigrant population, but this paper will also assess the feasibility of using tax data as a proxy for the unauthorized immigrant population in other states.