President Barack Obama was re-elected president Tuesday night, put over the top by the crucial battleground state of Ohio following the most expensive election in U.S. history.
"You made your voice heard, and you made a difference," Obama told supporters.
"I will return to the White House more inspired and more determined than ever," he said. 'We've got more work to do."
Obama and his family walked onto stage at his Chicago headquarters to the strains of Stevie Wonder's "Signed, Sealed, Delivered." The crowd welcomed him by chanting, "Four more years!"
A roar of approval thundered through the crowd after NBC reported that Ohio had gone to Obama. The victory in Ohio put Obama at 274 electoral college votes, four more than needed.
"This happened because of you. Thank you," Obama tweeted to supporters. It was retweeted more than more than 318,000 times, a record. A picture posted around 11 p.m. EST on Obama's Facebook page showing him hugging first lady Michelle Obama under the headline "Four more years" was liked by more than a million users.
Mitt Romney was silent for more than an hour after Ohio was projected for Obama. But he then conceded in a phone call to Obama.
"I have just called President Obama to congratulate him on his victory," Romney told disappointed supporters. "I wish all of them well, but particularly the president, the first lady and their daughters. This is a time of great challenges for America, and I pray that the president will be successful in guiding our nation."
Earlier, Pennsylvania, Wisconsin and New Hampshire went to Obama, according to NBC News, and Romney took North Carolina. Obama also won Virginia, Ohio and Colorado. Votes were still being counted in Florida.
After the Obama victories in Pennsylvania and Wisconsin, U.S. stock futures turned down and stayed lower with the Ohio vote results. (Click here for the latest prices.)