A rep for the musician confirmed the couple's happy news to Us Weekly on Tuesday.
"We are so thrilled and feel blessed to bring another little angel into our world," Rooney said in a statement.
Rooney and former Miss USA contestant Fallon have been married since April 2006. The couple have two other children, son Jagger and daughter Raquel.
"Jagger and Rocky are very excited, too," the musician continued. "They're going to make a great 'big brother - big sister duo' as the Rooney circus continues."