South Carolina mother Kayla Dillard said on Facebook that the man paid $540 in cash for all the girls' cookies, saying he did it "so y'all can get out of this cold" outside a store near Greenville.
The man first bought seven boxes of cookies before going back to buy all of them.
WYFF-TV reports that the man posed for a picture with two Girl Scouts last week, but no one got his name. Dillard said she still hasn't been able to confirm his identity.
Greenville is about 140 miles northeast of Atlanta.
The Associated Press contributed to this report.