( CNN ) -- The undocumented immigrant population in the United States rose to an estimated 11.7 million in 2012 , up from 11.5 million in 2011 , according to report released by the Pew Research Center Hispanic Trends Project . The number includes those who crossed U.S. borders illegally , as well as those who came in with temporary visas but stayed past their expiration date , Pew said Monday about its estimate , based on U.S. government data . Mark Hugo Lopez , director of Hispanic research at Pew and co-author of the study , says the data available can not point to a particular cause for the increase , but he says the improving U.S. economy could be a factor . According to Pew , in 2007 , there were an estimated 12.2 million undocumented immigrants in the United Sates . The number decreased to 11.3 million by 2009 , breaking a rising trend that had held for two decades . One reason for the decrease could have been the recession . In 2009 , the Center for Immigration Studies , a Washington-based think tank that seeks a `` pro-immigrant , low-immigration vision , '' said Census data indicated that more than 1 million undocumented immigrants left the previous year , a departure that began even before the nation 's economy took a turn for the worse . Immigrants from Mexico are still the largest group within the undocumented population -- 52 % as of 2012 -- but the number of recent Mexican immigrants has decreased at higher rates than the general group . That signals a shift in the demographic makeup of those entering illegally into the United States . `` They are coming from all parts of the world other than Mexico . Central American immigrants are a part of that , but so are immigrants from Asia and Europe , '' Lopez said . `` The report points to border apprehension trends , too -- the number of Mexicans apprehended at the border by the border patrol is down in the last year or so . '' Pew estimated there are now about 6 million Mexican undocumented immigrants in the United States . Lopez said that Southern states such as Georgia and North Carolina have seen an increase in undocumented immigrants because their economies have fared better than California since the 1990s . Texas , a state that weathered the recession better than others , was the only state that did n't see a drop in undocumented immigrants in the past few years . According to Pew , its methodology `` compares a demographic estimate of the number of immigrants residing legally in the country with the total number of immigrants as measured by a survey . '' The difference is assumed to be the number of unauthorized immigrants in the survey , a number that is later adjusted for omissions from the survey . The new data could also affect the debate on a potential comprehensive immigration reform which has stalled in the House of Representatives after the Senate approved a bill earlier this year that would provide a path to citizenship to those living here illegally . CNN 's Cindy Y. Rodriguez contributed to this report .
Undocumented immigrant population rose to 11.7 million in 2012 . Number represents those who crossed the U.S. borders illegally and those who overstayed their visas . States such as Georgia and North Carolina have seen a population increase . New numbers could affect the debate on potential comprehensive immigration reform .