The Millers had an option to extend the 28-year-old’s contract by an extra year but chose not to following his transfer request in January.
Ladapo stunned the club by asking to leave during the transfer window without any confirmed interest from other clubs.
He was forced to stay at the AESSEAL New York Stadium and returned to the fold but was exiled from the squad for the final three games of the season as Paul Warne’s side went on to win promotion..
The Millers opted not to trigger an option on Ladapo’s deal that would have meant they could demand a fee this summer and instead he will leave the club on a free transfer.
Ladapo, who joined from Plymouth in 2019, scored 40 goals in 123 appearances for the Millers.
Joe Mattock, Angus MacDonald and Mickel Miller have also been released.
The club have triggered options on the contracts of Viktor Johansson and Chiedozie Ogbene along with youngsters Josh Chapman and Jake Hull.
They are also discussing the prospect of a new long-term deal with Ogbene following his scintillating form last season.
Rotherham are also in discussions with Michael Smith, Michael Ihiekwe and Jamie Lindsay over new deals.