Trump also claimed FBI officials investigated a voter-canvassing operation in Muskegon, Michigan, where canvassers admitted submitting voter-registration applications with fake names.
The incident did not result in illegitimate ballots being cast and was caught by the local clerk.
He said the Department of Homeland Security identified more than 270,000 noncitizens on voter rolls in four states, without explaining how the agency identified them.
There are over 211 million registered voters in the US.
The US Constitution gives states control over elections, not the president.
But Trump's most concerning statement came near the end of his speech, when he said his administration would take more action to try to take control over elections.
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He announced the Department of Homeland Security would hold a briefing the next day to discuss vulnerabilities in state voting systems and would order states to remove noncitizens from the rolls.
