New York, Dec 1 : The total foreign-born population in the US, legal and illegal, was 49.5 million in October 2023, -- a record 4.5 million increase since President Joe Biden took office in 2021, a study by a Washington-based think tank found. At 15 per cent, the immigrant or foreign-born share of the US population is also the highest ever recorded in American history, the Center for Immigration Studies said, citing an October 2023 survey by the Census Bureau. As a debate rages in the country over the ongoing border crisis, the study showed that the 4.5 million increase is larger than the individual populations of 25 US states. The foreign-born population has grown on average by 137,000 a month since Biden took office, compared to 42,000 a month during Donald Trump's presidency before Covid-19 hit, and 68,000 a month during Barack Obama's two terms. Based on the think tank's prior estimates of illegal immigrants, more than half of the 4.5 million increase in the foreign-born population since January 2021 is likely due to illegal immigration. From January 2021 to October 2023, there have been roughly eight million 'encounters' at US borders, according to Customs and Border Protection. Court records and other information on the Department of Homeland Security (DHS) websites indicate that about 2.6 million (possibly 2.7 million) inadmissible aliens have been released into the country since the start of the Biden administration. While a large share of the recent foreign-born growth is attributed to illegal immigration, legal immigrants still account for three-fourths of the total foreign-born population. A significant number of new illegal immigrants, and perhaps a majority before the current border surge, were admitted legally on a temporary visa or under the visa waiver program and then did not leave the country when the time limit expired, the study said. The Department of Homeland Security for FY 2022 showed 850,000 foreign visitors overstayed their authorised stay in that year. The largest percentage increases since January 2021 were for immigrants from South America (up 28 per cent); Central America (up 25 per cent); Sub-Saharan Africa (up 21 per cent); the Caribbean (up 20 per cent); and the Middle East (up 14 per cent). Immigrants from all of Latin America increased by 2.9 million since January 2021, accounting for 63 per cent of the total increase in the foreign-born. The foreign-born in Census Bureau data included all persons who were not US citizens at birth, mainly naturalised citizens, lawful permanent residents, long-term temporary visitors, and illegal immigrants. /IANS