The exit of long-serving defender Andy Considine had been known for some time, but the club have also decided not to renew the deals of three other senior players.
Midfielder McGeouch and Ojo, who played intermittently for the club, will leave, as does forward Michael Ruth, who came through the youth academy.
Aberdeen manager Jim Goodwin told the club’s website: “We are very much in a transitional period where a number of players, some of whom who have had a long association with the club, must now move on for one reason or another.
“It is never an easy decision to make but having had time to assess the squad in the latter part of the season, these decisions have been taken to enable us to build a competitive first team for next season and ensure there are brighter days ahead.
“The hard work has already begun to identify the types of players required to take this great xlub back to where it belongs. The new players will add a freshness to the group, and much needed competition for places.
“As much as the 2021/2022 season is still a bit raw, we can’t change it. We must learn from the mistakes that were made and look forward to the 2022/2023 season with excitement and optimism.”