Genarlow Wilson has been in prison for two years for taking part in the sex act when he was 17 years old.
"This boy is not only her son, he's your son, he's my son," Sharpton told the cheering crowd from the steps of the Douglas County Courthouse. "We're here today because what affects you affects all of us."
State Rep. Alisha Thomas Morgan said Wilson's punishment was excessive and should be reduced, just like the prison sentence for former White House aide I. Lewis "Scooter" Libby, which was commuted Monday by President Bush.
"Genarlow is the face of many other young black men who have received injustice," Thomas Morgan said. "Somebody's got to stand up for them."
The crowd held signs that read "Free Genarlow" and "Justice Now." The issues of race and class came up in many speeches.
"If he had a different complexion and a different connection, we wouldn't be here," Sharpton said.
Wilson, now 21, is serving a 10-year mandatory sentence for aggravated child molestation stemming from a 2003 New Year's Eve Party where he was captured on videotape receiving oral sex from a 15-year-old girl. The law has since been changed by Georgia lawmakers, but the state's top court said the new law could not be applied retroactively.
Wilson was also charged in 2003 with raping a 17-year-old girl at the party, but a jury acquitted him of the charges.
Five other male partygoers accepted plea deals in the case. Wilson rejected the plea offer.
On June 11, Monroe County Superior Court Judge Thomas Wilson ruled that Genarlow Wilson should be freed from prison and not listed on Georgia's sex offender registry. The judge called the 10-year mandatory sentence "a grave miscarriage of justice" that violated the constitution.
Attorney General Thurbert Baker immediately appealed that ruling, drawing criticism from civil rights activists.
The Georgia Supreme Court is set to hear the latest appeal in October. Wilson's lawyer, B.J. Bernstein, had sought to get Wilson released on bond while the appeal moved forward.
But Douglas County Superior Court Judge David Emerson said Wilson was ineligible for bond under Georgia law. Bernstein is appealing that decision.