Tens of thousands of people, young and old, black and white, Asian and Latino from many different states flocked to the National Mall where millions will gather to soak up a moment of change and history.
The Secret Service launched its final security sweep of the area at 3am and an hour later special underground Metro trains were already filled to capacity and darkened roads into the city were packed with traffic.
Transport officials warned that the subway system would be crowded and bicycles were barred from central Washington. Inauguration-goers struggled to navigate a maze of security that has seen large blocks of the city closed to traffic and police and army guards on patrol.
Late-night revelers partied into the morning, after bars and clubs stayed open until 4am and exhausted staff struggled to serve the new surge in clientele.
Some parking attendants were seen jumping up and down to keep warm but the below-freezing temperatures did not deter the crowds eager to witness the historic moment when Obama takes the oath of office at 12 noon (9pm UAE time).
"We woke up at three but it's worth it," said Mary Lloyd. "I think it's history on its way. We just want to be there celebrating."
Others, like Prat Pathak who rose early to get a good viewing spot for the parade, hoped that Obama would "fix the economy because that's the root of a lot of what's going on in the US."
A police spokeman said that as of 6am, things were "going fine" with no crimes or other incidents to report in the areas around the inauguration.
Along Pennsylvania Avenue, where Obama will ride with President George W Bush before the inauguration, there stood rows of seats and camera crews braved a whipping cold wind to set up their equipment.
Long rows of green "porta-potty" temporary toilets also were prepared to welcome the vast crowds.
On an office building at the juncture where Pennsylvania Avenue makes a turn toward the Capitol, two large banners were fixed where they would be seen by the current and future president.
"Welcome Mr President," said one. "Thank you Mr President," said the other.
Past racial struggles were on many minds, hours before Obama swears to "preserve, protect and defend" the US constitution and shatter America's most enduring color barrier as the first black president.
Elizabeth Brooks, an African-American and Washington resident of 30 years, gazed at the white dome and flag-draped columns of the US Capitol, where Obama will take the oath of office, meditating on a racial circle about to close.
"I am remembering the four little girls that were bombed in the 16th Street Baptist church in Alabama," she said, remembering the 1963 attack by white racists in segregated Birmingham in which all four girls perished.
"We have two little girls going into the White House tomorrow in their place," she said, her eyes filling with tears, speaking of Obama's young daughters Malia and Sasha.
Renita King, 46, told her six-year-old son Arthur to say a silent prayer for Obama, and said she had flown from Houston, Texas for the inauguration to mark the years of racial prejudice endured by her 73-year-old mother.
"She never thought she would see this. I am here for all the floors she has cleaned and waxed," she said.
"I am here for her, and every time that she was called a nigger -- that is how I see this, as an American."