Estimating Unauthorized Immigrant Populations in Sub-State Areas

Laura Hill, Public Policy Institute of California (PPIC)
Hans Johnson, Public Policy Institute of California (PPIC)
Joseph M. Hayes, Public Policy Institute of California (PPIC)
David Ezekiel, Public Policy Institute of California (PPIC)

The United States is home to approximately 11 million unauthorized immigrants. Careful estimates at the state level are published regularly, but these do not describe the distribution of the population within each state. We have developed the first-ever estimates of the nation’s unauthorized immigrant population by county and zip code. We 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 calendar years 2001-2009, and we have used these to estimate the geographical distribution of undocumented immigrants within states through 2008. This paper will extend the analysis to 2009, examining what impact the recent decline in the estimated population has had on its distribution within each state.