The former Manchester City youth team star had been in discussions about extending his stay at Chorley, but has decided to leave.
The 25-year-old defender joined in 2018 and was in his second spell at Victory Park after initially playing for the club in 2016.
He was voted supporters’ player of the year during the National League North promotion-winning campaignof 2018/19, before scoring the opening goal othis season 2019/20 National League season at Sutton United.
Chorley boss Jamie Vermiglio said: "Over the past few weeks we have been in discussions with Courtney about his future.
"He is a player who has done fantastically for our club since his return and we think he still could have helped us out and improved next season; therefore we offered him a deal to stay.
"Unfortunately, Courtney feels that his football future lies elsewhere and we respect his decision. We thank Mepps for everything he’s done for Chorley, particularly during our promotion-winning season."
The former Stockport County man leaves the Magpies after making 96 appearances and scoring nine goals.