The midfielder and the club have failed to reach an agreement over a new contract.
The 26-year-old will become a free agent on July 1 and will be able to join another club.
He has been linked with a move to newly-promoted York City.
“Following negotiations with Jak McCourt, the two parties have been unable to reach an agreement over a new contract,” the Spireites said in a statement.
“The midfielder will therefore leave the club following the expiry of his contract at the end of this month.
“Jak, who is in his second spell with the Spireites, will leave with the club’s thanks for his service and best wishes for the future.”
McCourt follows Jim Kellermann and Luke Croll in leaving Town this summer after failing to agree new terms.
After a previous spell at Chesterfield in the 2017/18 season, McCourt rejoined the Blues in December 2020 on a short-term contract before signing an 18-month deal.
He made 22 appearances in all competitions last season.
Along with McCourt, Kellermann and Croll, striker Tom Denton was set to be offered a new contract but we are yet to hear whether he has decided to stay.