He said it was "really convenient" but joked, "I can't tell you who I voted for."
Obama followed regular voting protocol, signing the needed forms and showing his driver's license at a South Side Chicago voting site. He then voted at a blue voting machine.
It was the first time a sitting presidential nominee voted early and reflects the Obama campaign's strategy
to encourage as many voters as possible to vote early or by absentee ballot.
About 35% of the electorate is expected to vote before Election Day.
Obama made the Chicago stop while on a tour meant to drum up support in the all-important swing states.
Colorado, Florida, Iowa, North Carolina, New Hampshire, Nevada, Ohio, Virginia and Wisconsin are considered traditionally "purple," and like in many previous election campaigns in the United States, neither Obama nor Republican challenger Mitt Romney
have been able to create a substantial lead in any of them.
peg Obama and Romney in a neck-to-neck race, with Romney clinging to a 1% lead over Obama – 47% to 46%.
Meanwhile, the Washington Post has officially endorsed Obama, as it did in 2008.
In its Thursday editorial, the Washington Post said that while much of the campaign for the White House has "dwelt on the past," Obama is in a better position to lead the US "on a solid financial track after a bruising recession."
But the influential daily stressed what it called "the disappointments" of the president's first term in office.
"We come to that judgment with eyes open to the disappointments of Mr. Obama's first term. He did not end, as he promised he would, 'our chronic avoidance of tough decisions' on fiscal matters.
"But Mr. Obama is committed to the only approach that can succeed: A balance of entitlement reform and revenue increases," the Post said.
Obama was also endorsed Thursday by former US Secretary of State Colin Powell – a leading Republican figure.
The former four-star general, who served under President George W. Bush,
endorsed Obama in 2008, as well.
Both endorsements were made to the dismay of his fellow Republicans, prompting him to explain that he "likes to get all the facts and see exactly what each candidate will do during their campaigns before making his decision on who to vote for."
Speaking with CBS News Powell said: "I think I'm a Republican of a more moderate mold... That's something of a dying breed I'm sorry to say."
Sharon Gilad and news agencies contributed to this report