WASHINGTON: There were about 725,000 Indian illegal immigrants in the US -- the third largest population of unauthorised immigrants after Mexico and El Salvador, according to new Pew Research Centre 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 Washington-based think tank said.

Almost every region in the world had a notable increase in the number of unauthorised immigrants in the US from 2007 to 2021, with the largest increase from Central America (240,000) and South and East Asia (180,000).

While the number of unauthorised immigrants from Mexico living in the US -- 4.1 million in 2021 -- was the lowest since the 1990s, El Salvador -- 800,000 -- and India with 725,000 immigrants saw an increase in the numbers, the report said.

Among countries with the largest numbers of US unauthorised immigrants, India, Brazil, Canada and former Soviet Union countries all experienced growth from 2017 to 2021, the report said.

The six states with the largest unauthorised immigrant populations in 2021 were: California (1.9 million), Texas (1.6 million), Florida (900,000), New York (600,000), New Jersey (450,000) and Illinois (400,000), the report said.

In 2021, the population of unauthorised immigrants from other countries was 6.4 million, up by 900,000 from 2017, the report said.

Other countries which accounted for most unauthorised immigrants were Guatemala (700,000) and Honduras (525,000).

The report said India, Guatemala and Honduras all saw increases from 2017 with the unauthorised immigrant population in the US reaching 10.5 million in 2021, according to new Pew Research Centre estimates.

There were increases in unauthorised immigrants from nearly every other region of the world – Central America, the Caribbean, South America, Asia, Europe and sub-Saharan Africa.

Meanwhile, the lawful immigrant population grew by more than 8 million, a 29 per cent increase, and the number of naturalised US citizens grew by 49 per cent.

In 2021, naturalised citizens accounted for about half (49 per cent) of all immigrants in the country, the report said.