Factbox: Illegal immigration in the United States

(Reuters) - An Arizona immigration law that requires police in the U.S. state bordering Mexico to determine whether people are in the country illegally if there is "reasonable suspicion," has stirred a national furor and pushed immigration to the forefront of U.S. politics.

Here are some facts about illegal immigrants in the United States, together with some of the policy initiatives by federal and state governments to address immigration:

* There were an estimated 10.8 million illegal immigrants living in the United States on January 1, 2009.

* Most were from Latin America, with some 6.7 million from Mexico and 1.33 million from Central American nations El Salvador, Guatemala and Honduras.

* Arizona had a total population of 6.6 million in 2009, including an estimated 460,000 undocumented immigrants.

* The state is the principal corridor for illegal immigrants entering the United States from Mexico. The U.S. Border Patrol's Tucson sector has made an average of 650 arrests a day so far this year. Phoenix police reported 357 extortion-related abductions in 2007 targeting people with ties to Mexican smuggling rings.

* President Barack Obama backs a comprehensive overhaul of federal immigration laws. Any reform is seen as unlikely to pass Congress this year and Obama has said lawmakers may not have the appetite to tackle it before the November congressional elections. Some Democrats fear delay could cause a backlash among Latino voters.

* Obama supports a system that allows illegal immigrants who have otherwise obeyed U.S. law to pay a fine, learn English and become citizens; as well as tightening border security and clamping down on employers that hire undocumented workers.

* The last attempt to overhaul the U.S. immigration system, by Obama's predecessor, President George W. Bush, in 2007, was torpedoed by Bush's fellow Republicans in Congress.

* Arizona's law is the toughest but by no means the only immigration-related measure passed by U.S. states, which traditionally leave border security to the federal government.

* It requires state and local police officers to arrest those unable to provide documentation proving they are in the country legally. It also makes it a crime to transport someone who is an illegal immigrant and to hire day laborers off the street.

* In just the first three months of 2010, more than 1,180 bills and resolutions relating to immigrants and refugees were introduced in state legislatures across the country. Of those bills, 71 laws were enacted and 87 resolutions adopted in 25 states.

Sources: U.S. Department of Homeland Security, U.S. Census Bureau and the National Conference of State Legislatures.

(Reporting by Tim Gaynor; Editing by Peter Cooney)