Democratic presidential candidate Barack Obama returned to Chicago, the city where his rise to prominence began, Tuesday and cast his vote at 8:45 am (1345 GMT) at the Shoesmith School gymnasium, reported dpa.
Obama arrived at the polling station with his wife Michelle and daughters Malia and Natasha.
The Democratic candidate took his time, pausing to explain the process to his daughters at the booth, and prompting television commentators to joke: "Is he undecided?"
Obama, 47, who would be the first African American president in US history if elected, was the strong favourite heading into Tuesday's vote.
In largely Democratic Chicago, voters were supporting Obama and much of the fervour behind his candidacy here will come from his fellow African Americans, driving in part an expected 80-per-cent voter turnout rate.
Obama will also spend election night in Chicago, where officials expect up to a million people to gather in Grant Park to watch the results and hear from their candidate after votes are tabulated in his race against Republican John McCain..