The study by the Pew Hispanic Center says about 300-thousand people a year came to the U.S illegally between March 2007 and 2009. That's down from about 850-thousand annually from March 2000 through 2005.
Jeffrey Passel, who helped write the study, says fewer Mexicans are crossing illegally to the U.S., but says there's no data to suggest Mexicans already in the U.S are going home.
"In the case of countries other than Mexico, our data points very significant drops in the number coming to the United States. The number leaving may have gone up in the last several years compared with earlier in the decade," says Passel.
Recent studies by UCSD immigration researchers show people in Mexico are waiting for the U.S. economy to recover before they cross. The study also shows border enforcement does little to dissuade people from crossing illegally.