The Transportation Security Administration (TSA) said the singer was denied access to the US "on national security grounds" and would be returned to Britain on Wednesday.
Flight 919 from London to Washington diverted 600 miles to Bangor International Airport on Tuesday, landing at around 7.30pm British time, after US security officials were told Stevens was aboard.
United Airlines officials in London initially failed to spot his name, which he has changed to Yusef Islam - on the watch list, the TSA said.
Passengers, including British pop veterans Marillion, were at first told the diversion was due to refuelling. It eventually arrived in Washington six hours late.
Stevens, who was denied access to Israel four years ago, was detained and questioned, the TSA said. His 21-year-old daughter was allowed into the US.
A spokesman for United Airlines said the flight was diverted "to keep the aircraft from entering the north east corridor airspace".
Cat Stevens had a string of hits in the 1960s and 1970s, including Wild World and Morning Has Broken.
He abandoned his music career in the late 1970s and changed his name after being persuaded by orthodox Muslim teachers that his lifestyle was forbidden by Islamic law.



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