"We're so glad to be here, and even more glad to be here this evening," she told the audience at the Boardwalk Hall Friday night. "You know, after something like this, you wonder whether the show should go on. We thought, this building was still here, so it must be here for a reason."
The "American Idol" season four winner told the audience she would put her profits "right back into the community here," the Press of Atlantic City quoted her as saying.
"I wouldn't feel right making any money off of tonight's show," Underwood said.
After the concert, she took to Twitter to offer words of support to the hurricane-ravaged community.
"Thank you beautiful Atlantic City! You all made my year! You have been through so much and still rocked the house! I leave in awe! Thanks!" she tweeted.
The 29-year-old has been donating $1 of every concert ticket sold to the American Red Cross since September, The Hollywood Reporter said.