Clinton noted that the election she lost on November 8 to President-elect Donald Trump laid bare divisions in the United States.
"But please listen to me when I say this," she added. "America is worth it. Our children are worth it. Believe in our country, fight for our values and never give up."
The speech marked Clinton's return to public life after a loss to Trump that belied public opinion polls and corporate mainstream media pundits predicting an easy victory for the former secretary of state.
A heavy turnout in industrial states that have been hard hit by closed factories gave Trump votes in the US Electoral College that are needed to become president. Trump had secured the required 270 electoral votes to become the 45th president of the United States.