First recorded (as “My Girl Sloopy”) by The Vibrations (US #26/R&B #10 1964).
Other hit versions by Little Caesar & The Consuls (CAN #1/US #50 1965), The McCoys (US #1/UK #5 1965), The Ramsey Lewis Trio (US #11/R&B #6 1965).
Also re-recorded by Ramsey Lewis (1973).
From the wiki: “‘Hang On, Sloopy’ is a 1964 song owned by Wes Farrell and Bert Russell, originally titled ‘My Girl Sloopy’. A tale told around Columbus, Ohio, is that Sloopy was a waitress/singer, who used the name ‘Sloopy’ on stage. The truth is the song was never about her. It was written by a St. Louis teen who created a fictitious ‘Sloopy’ and then sold his publishing rights to Farrell and Russell.