New Delhi, Nov 22 : Numbering around 725,000, Indians form the third largest population of illegal immigrants in the US after Mexico and El Salvador, according to new Pew Research Center estimates. As of 2021, the country's 10.5 million unauthorised immigrants represented about three per cent of the total US population and 22 per cent of the foreign-born population, the research said. Mexico, which accounted for 39 per cent of the nation's unauthorised immigrants in 2021 numbering around 4.1 million, was followed by El Salvador (800,000); India (725,000); and Guatemala (700,000). While the number from Mexico dropped by 900,000 from 2017 to 2021, the number of illegal immigrants from other countries grew rapidly at the same time. In 2021, this population was 6.4 million, up by 900,000 from 2017. India, Brazil, Canada and former Soviet Union countries all experienced growth from 2017 to 2021. According to new data from US Customs and Border Protection, an unprecedented number of undocumented Indian immigrants are crossing the US borders on foot. From October 2022 to September 2023, 96,917 Indians were apprehended, expelled or denied entry for having entered the US without papers. Since borders opened after Covid, the number of undocumented Indians in the US went up with 30,662 encountered in the 2021 fiscal year and 63,927 in the 2022 fiscal year. Out of the nearly 97,000 encounters this year, 30,010 were at the Canadian border and 41,770 at the Southern border. The Pew research also found that overall, about 7.8 million illegal immigrants were in the US labour force in 2021. Among the US states, only Florida and Washington witnessed increases to their unauthorised immigrant populations, while California and Nevada saw decreases. Meanwhile, the lawful immigrant population grew by more than eight million -- a 29 per cent increase, and the number of naturalised US citizens grew by 49 per cent in 2021. /IANS