Undocumented Indian immigrants to the US, numbering over half a million, hold a collective spending power of USD15.5 billion and contribute USD2.8 billion to the federal, state and local tax revenue, says an American think-tank report. Using the latest available American Community Survey data from 2019 in its latest research, the new American Economy think-tank said undocumented Indian immigrants are the top third contributor to the US economy among other undocumented immigrants. There are 4.2 million immigrants from Mexico who lack documentation.