Town have confirmed the departures of out-of-contract quartet Freddie Sears, James Wilson, Emyr Huws and Tristan Nydam.
Sears, 31, had been expected to go having been in and out of the side this season. The striker had been with the Blues since January 2015 when he was part of the side which reached the Championship play-offs.
The former West Ham trainee made 151 starts and 66 sub appearances for the Blues, scoring 34 times.
Centre-half Wilson, 32, named Player of the Year at the weekend, joined the club in the summer of 2019 following a successful trial having left Lincoln City.
The once-capped Welsh international made 47 starts and two sub appearances, scoring twice.
Midfielder Huws, 27, joined the Blues initially on loan from Cardiff in January 2017 and impressed in the remaining months of that season, most famously scoring the third goal in the 3-1 win over Newcastle at Portman Road.
The Wales international joined on a permanent basis that summer on a free transfer but injury limited his involvement in the following campaigns and his exit comes as little shock.
Overall, the former Manchester City youngster made 43 starts and 12 sub appearances, scoring five goals.
Nydam, 21, came through the academy but saw his progress hit by a broken leg and damaged ankle ligaments suffered in pre-season ahead of 2019/20.
The Zimbabwe-born Colchester-raised midfielder returned to first team action last month and looked to have caught manager Cook’s eye, so it had been anticipated that he would win a new deal.
Overall, the former England U19 international made 14 starts and eight sub appearances for the club having come through the academy.
As reported earlier, Town have taken the options on Kayden Jackson and Janoi Donacien’s contracts and they are yet to make announcements on Teddy Bishop, Toto Nsiala, Gwion Edwards, Aaron Drinan, Ben Morris, Idris El Mizouni, Liam Gibbs, Bailey Clements, Levi Andoh, Bert White and Tommy Hughes.
Of those, Town have options to keep Bishop, Nsiala, Morris, El Mizouni, Clements, Andoh, White and Hughes.
We understand Bishop has made enough appearances to automatically trigger an additional year with the Blues and a number of other players' options have also been exercised. As previously reported, young midfielder Gibbs has already been offered a contract.
Manager Cook, who has made little secret of his frustrations and dissatisfaction with the players he inherited, met with the squad individually today.
TWTD understands that in addition to the released out-of contract players, a number of those whose deals still have time to run have been told that the club will listen to offers should they come in.
Meanwhile, departing loanees Mark McGuinness and Troy Parrott have tweeted their thoughts as they leave the Blues.