An analysis by the Center for Immigration Studies of monthly data collected by the Census Bureau shows that fewer illegal immigrants are coming and more are returning home. The findings also show that the legal immigrant population has not declined. As a result, the overall foreign-born population has held relatively steady. The report examines the extent to which stepped-up enforcement and the downturn in the economy account for this trend.

The report, "A Shifting Tide: Recent Trends in the Illegal Immigrant Population," is written by Steven Camarota, the Center's Director of Research, and Karen Jensenius, the Center's Demographer.

Among the findings:

- Our best estimate is that the illegal population declined 13.7 percent (1.7 million) from a peak of 12.5 million in the summer of 2007 to 10.8 million in the first quarter of 2009.

- If we compare the first quarter of 2007 to the first quarter of 2009, the implied decline is 1.3 million (10.9 percent). In just the last year the decline was 5.7 percent.

- By design, these estimates produce results similar to those from the Department of Homeland Security (DHS). DHS estimates of the illegal population show a 1.5 percent decline between January 1, 2007, and January 1, 2008. Our estimates show a 1.6 percent decline over the same time period. DHS has not yet estimated the illegal population for January 2009.

- There is evidence that the number of new illegal immigrants arriving has fallen by about one-third in the last two years compared to earlier in this decade.

- There is also evidence that the number of illegal immigrants returning home has more than doubled in the last two years compared to earlier in this decade.

- While migration patterns have fundamentally changed, it must be remembered that the overwhelming majority of illegal immigrants have not left the country, and tens of thousands of new illegal immigrants continue to settle in the country each year.

- Our analysis shows that only the illegal immigrant population has declined. The legal immigrant population does not show the same decline. This is true overall and for Mexico specifically, the top illegal-immigrant-sending country.

- The fact that the legal immigrant population does not show the same decline is an indication that stepped-up enforcement has played a role.

- Another indication that enforcement has contributed to the decline is that the illegal immigrant population began falling before there was a significant rise in the unemployment rate for illegal immigrants.

- While the decline began before unemployment among illegal immigrants rose, since then unemployment among illegal immigrants has increased dramatically and must now be playing a significant role in reducing their numbers.

- There is evidence that the illegal population rose in the summer of 2007, while Congress was considering legalizing illegal immigrants. When that legislation failed to pass, the illegal population quickly began a dramatic fall.

- There is no way to know if the current trend will continue. Given President Obama's stated desire to legalize illegal immigrants and his backing away from enforcement efforts, it seems likely that when the economy recovers, the illegal population will resume its growth.