According to new estimates, the number of undocumented immigrants living in the United States remained steady between 2009 and 2010, following a two-year period of decline that began in 2007. A study released Tuesday by the Pew Hispanic Center found that as of March 2010, there were approximately 11.2 million undocumented immigrants in the U.S., compared with 11.1 million a year earlier and a peak of 12 million in 2007. Similarly, the number of undocumented immigrants in the nation’s workforce remained steady at 8 million in the 2009-2010 period, compared to 8.4 million in 2007. The decline was notable particularly in Colorado, Florida, New York, Virginia, Arizona, Nevada, and Utah.

Although the Pew report was not designed to answer why these changes occurred, Pew Hispanic Center director Paul Taylor said “common sense” suggests that the economic recession and slow recovery from it in the U.S., as well as tougher border enforcement, are contributing factors. Senior demographer and co-author of the report Jeffrey S. Passel told Reuters that, in the past, immigration inflows have been tied to the state of the U.S. economy, particularly in the case of Mexico. Undocumented immigrants from Mexico account for 58 percent of the total and appear to be a primary source of the decline.

Despite stricter border enforcement and record numbers of deportations under the Obama administration (392,000 in 2010), the report did not find that a large number of undocumented immigrants were leaving the country. This may yet again prove the failure behind state-by-state “attrition through enforcement,” a strategy in which states adopt tough, anti-immigration laws. Although the anti-immigrant SB 1070 law passed in Arizona in 2010 is currently on hold pending court appeals, at least 15 other states have proposed similar legislation in 2011.

The Pew analysis, which is based on U.S. census data, also reports that 350,000 children had at least one undocumented-immigrant parent in 2009. This represents about 8 percent of the newborn population and is on par with figures from 2008. Conservative lawmakers in Congress and state legislatures have proposed initiatives to deny automatic citizenship to the children of undocumented immigrants, and in December 2010, a Senate filibuster blocked passage of the DREAM Act, federal legislation that would have provided children of undocumented immigrants permanent residency conditioned upon completion of two years of higher education or military service. Birthright citizenship is currently guaranteed by the 14th amendment to the U.S. constitution.