The big defender returned to the club only a few months after he left Dingwall for the Dons.
Paperwork was completed on an 18-month contract which was agreed by all parties to see the player return to Jim McIntyre's men.
Quinn made the move east when he became a free agent last year, but he was thought to be homesick and disappointed by a lack of first-team opportunities.
He slotted into the Aberdeen squad after signing a two-year deal in summer 2915, and became a fans' favourite when he netted the winning goal against Celtic in September.
The move had been arranged in December but was pushed to the back burner when the sides met each other in the league on January 17.
Aberdeen won that fixture 3-2, and Quinn has since gone on to score another crucial goal against Celtic as County demolished the Glasgow side in the League Cup semi-final.
Source: STV