Washington (CNN) -- After celebrating his second inauguration with a throng estimated at about 800,000, President Barack Obama and first lady Michelle Obama spent the evening at more intimate affairs: 30,000 guests at two inaugural balls.
The Obamas first swung by the Commander in Chief's Ball, where they danced in front of a sea of cell phone cameras to Jennifer Hudson's performance of Al Green's classic "Let's Stay Together." They then switched partners: the first lady danced with Marine Corps Gunnery Sgt. Timothy D. Easterling and the president danced with an Air Force Staff Sgt. Bria D. Nelson.
Obama sang a bit of the same song at a campaign fundraiser in Harlem last year.
The first lady wore a custom, ruby-colored gown designed by Jason Wu, who also designed her inaugural gown in 2009, and the president wore a tuxedo and white tie.
Vice President Joe Biden and his wife, Jill, also appeared at the two balls, dancing to Jamie Foxx performing Ray Charles' "I Can't Stop Loving You." Foxx portrayed the singer in the movie "Ray."
The Bidens also switched partners with military members, the vice president dancing with Army Staff Sgt. Keesha Nicole Dentino and Mrs. Biden with Navy Petty Officer Patrick Figueroa.
Obama delivered the "thanks of the American people" to the members of the military at the service members' ball.
"Thank you for volunteering, thank you for stepping up, thanks for making us strong, thank you for keeping us safe," the commander-in-chief told the cheering revelers.
He also told them that Joint Chiefs Chairman Gen. Martin Dempsey had promised to sing, "so hold him to that."
The Obamas also danced to "Let's Stay Together" at the Inaugural Ball, also held in the convention center.
Hudson was one of 21 acts that were to perform at the two balls, including Alicia Keys, Brad Paisley, Far East Movement, fun., members of the cast of "Glee," John Legend, Katy Perry, Marc Anthony, Mindless Behavior, Nick Cannon, Smokey Robinson, Soul Children of Chicago, Soundgarden, Stevie Wonder and Usher.
Keys changed the lyrics of her hit "Girl on Fire" from "This girl is on fire" to "Obama's on fire."
Organizers converted the convention center's massive, bare-bones exhibit hall into a slightly less bare-bones ballroom. No chandeliers here, just a few drapes and decorations to spruce up the exposed ceiling and fluorescent lights. Revelers danced on the center's industrial concrete floor.
Seen close to the stage were the first lady's mother, Marian Robinson, and Obama adviser and family friend Valerie Jarrett. Former Obama campaign manager Jim Messina was seen in the crowd.
The Inaugural Ball was split between two floors in the building, and attendees were not allowed to go from floor to floor.
While Monday's events were the only two official balls, there were others in the city around the inauguration.
On Sunday night, they included the Red, White and Blue Ball headlined by Lynyrd Skynyrd; the Hip Hop Ball, chaired by Russell Simmons with appearances by 2 Chainz, John Legend, Eva Longoria and Swizz Beatz; and the "Latino In Performance" and "Let Freedom Ring!" galas at the Kennedy Center.
On Monday, the Creative Coalition was putting on a ball with a performance by the Goo Goo Dolls, while the Young and Powerful Black Tie Ball and the Congressional Black Caucus Inaugural Ball were also taking place in the city.
Sponsors threw a ball for George Washington a week after his inauguration in New York in 1789, but the celebrations were established as a tradition with the inauguration of James Madison in Washington in 1809.
The Obamas dashed around Washington to 10 balls in 2009, but like many things in his second inauguration -- smaller crowds, shorter lines, shorter speeches -- the number was reduced.
President Bill Clinton's second inauguration in 1997 holds the record for most balls with 14. George W. Bush had eight balls in 2001 and nine in 2005.
CNN's Allison Brennan, Alison Harding and Lesa Jansen contributed to this report