The former Norwich striker scored 10 goals in just 17 starts but struggled for fitness all season and has not been offered a new contract.
Also shown the door at Sixfields are defenders Paul Rodgers and Marcus Hall, winger Francis Laurent and youngsters Courtney Herbert, Alex Konstantinou and Seb Harris.
Forwards Billy McKay and Guillem Bauza have been offered new deals, along with midfielders Greg Kaziboni and Kevin Thornton and goalkeeper Paul Walker.
No decision has yet been taken on goalkeeper Chris Dunn, defender Dean Beckwith and winger Liam Davis, while Steve Collis, Seth Nana Ofori-Twumasi, Byron Webster, Ben Tozer and Josh Walker have returned to their parent clubs after their loan spells ended.
Assistant manager Malcolm Crosby will also be leaving with Johnson set to appoint a new number two later in the summer.
Source: PA
Source: PA