Trevor Carson, Jack Deaman, Omari Sterling-James, Matt Taylor, Lee Vaughan and Jamal Lawrence are all on the list.
Johnson also informed Durrell Berry, Craig Braham-Barrett, Troy Brown, Danny Haynes, Mathieu Manset, Matt Richards and Matt Gould they would not be offered new contracts at this time.
Winger Andy Haworth, who spent the second half of the season on loan at Barrow, has also been released.
Long term absentees Asa Hall, Jordan Wynter and Eliot Richards – who are all contracted until the end of next season – will be assessed during pre-season and decisions will be made then.
Loanees Wes Burns, Will Packwood, Shaun Harrad and Matt Sparrow have all departed after their temporary spells with the Robins.
That leaves Zack Kotwica, Joe Hanks, Bobbie Dale, James Bowen and Harry Williams as players who are contracted for next season and feature in Johnson's plans.
Russell Milton has been confirmed as Johnson's assistant manager for next season, with negotiations currently ongoing with the rest of the backroom staff.