"I voted for a guy named Trump," the president told reporters.
President Trump has cast his vote for November's presidential election early and in-person.
After completing his ballot in the key state of Florida, he spoke to reporters at the Palm Beach polling station, telling them: "I voted for a guy named Trump."
He repeated his argument that that voting in person is more secure than by post - a claim which he's never been backed up with any evidence.
"It was a very secure, but much more secure than when you send in a ballot, I can tell you that. Everything was very strict. Right by the rules. When you send in your ballot, it could never be like that," he said.
The president switched his official residence from New York to his private Florida club last year, complaining that New York politicians had treated him badly. Since the switch, he has also voted twice by post.
Voters in New York also began to cast their ballots in person on Saturday, with thousands assembling early in the morning in Madison Square Garden.
More than 54 million votes have been cast so far, with around an additional 100 million expected before a winner is declared.
The election is officially held on November 3 but this year, with so many postal votes, the result may not be known for days or even weeks afterwards.