The Robins sat second from bottom when the 49-year-old replaced Sean O'Driscoll at Ashton Gate back in December and remained in the drop zone until early February.
However, a memorable three months saw City lose just three times in their remaining 20 league fixtures, culminating in a mid-table finish, and Cotterill hailed the spirit of his troops for the turnaround.
Speaking to Sky Sports News following the 1-1 draw with Crawley Town on the final day of the season, the manager said: "To finish in the top half of the table is a wonderful achievement. It was a great effort from everyone connected with the club.
"The boys never gave up and it's great testament to their spirit. We have already started something and now I have to try to bring other players into the squad."
Jamie Proctor's first-half strike had given Town a slender lead, only for Nottingham Forest loanee Simon Gillet to restore parity midway through the second half.