According to Department of Homeland Security statistics, there were an estimated 460,000 unauthorized immigrants in Arizona in January 2009. That statistic, making Arizona the state with the seventh largest illegal immigrant population, was often cited last week, as Gov. Jan Brewer signed the nation’s toughest law on illegal immigration.

The number comes from “Estimates of the Unauthorized Immigrant Population Residing in the United States,” a report that the DHS releases each year, but sadly does not add to Data.gov. It takes a little digging to find it, but the most recent report for January 2009 (released in January 2010) can be viewed in a PDF format by going to DHS.gov, clicking on “Immigration” and scrolling down to “Immigration Statistics” and then clicking on “Publications,” then scrolling to “Annual Population Estimates.”

The report found that while the number of unauthorized immigrants in Arizona grew from 330,000 in 2000 to 460,000 in 2009, the percent of unauthorized immigrants of the total state population remained the same at 4 percent. The state with the largest number of illegal immigrants in 2009 was California, with 2.6 million, followed by Texas with 1.7 million, Florida with 720,000, New York with 550,000, Illinois with 540,000, Georgia with 480,000.

The report also details how DHS calculates this number. In a nutshell, they take the total number of the foreign-born population living in the United States on January 1, 2009, as calculated by the U.S. Census Bureau, and subtract the total legally resident population on the same date, as tracked by DHS.

While neither this report, nor the underlying data is on Data.gov, the DHS has put up other data on Data.gov that likely comprises their calculations for the total legally resident population, including several tables that track the number of non-immigrants admitted into the United States using Form I-94, the number of people obtaining legal resident status, and nonimmigrant temporary work admissions.

Other immigration-related data from DHS on Data.gov include data on those who have sought petitions for naturalization and those granted and denied, immigrant orphans adopted by U.S. citizens, refugee arrivals by country of nationality, individuals granted asylum, and those obtaining legal permanent resident status from 1820 to 2008.

Another interesting report relating to emigration is the Quarterly Publication of Individuals Who Have Chosen to Expatriate, published by the Department of Treasury in the Federal Register which lists each new person who has given up their U.S. citizenship.

Sadly this list is also does not appear to be on Data.gov, but it can be found on the Federal Register website.

A recent New York Times article found that the number of people renunciations of U.S. citizenship has grown from 235 in 2008 to 743 in 2009.