The Indianapolis Star reported Ryan's friends, including actress Kathy Najimy, and Mellencamp's teen-age sons, Hud and Speck, attended the surprise party Saturday night at Downtown's Dunaways before they headed off to Clowes Memorial Hall to watch Mellencamp's show.
Connie McDonald, office and events manager for Dunaways, told the newspaper the group enjoyed dinner, followed by Ryan's birthday carrot cake.
"It was really, really sweet, you know," McDonald said of the event.
Mellencamp began dating Ryan late last year. His divorce from fashion model Elaine Irwin was finalized in August. Mellencamp and Irwin were married in 1992.
Ryan was previously married to actor Dennis Quaid.