The 25-year-old midfielder has joined the Spireites on a free transfer after leaving the Greens by mutual consent.
Cooper will be most remembered by Argyle fans for his 12 assists in the 2019/20 season when they won promotion from League Two.
Schumacher said: “I wish George all the best in his next football challenge.
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"I will fondly remember all of his assists in the 2019/20 promotion season, where if it hadn’t of been for his free kick goal against Morecambe when the game was really tight, or his long-range pass that set Ryan Hardie off against Macclesfield, then the points per game ratio could have been different.”
Cooper came through the ranks at Crewe before his form landed him a move to Peterborough United for an undisclosed fee.
He was loaned out to Plymouth and his impressive performances persuaded them to turn the move into a permanent deal.
But unfortunately Cooper picked up a serious injury in December 2020 and he has struggled fitness-wise since, making just three appearances last season.
But it is hoped a move away and a fresh start will help Cooper kick-on and find the form from a couple of seasons ago.
"Over the last two seasons it’s been hard for George getting over a number of injuries,” Schumacher added.
"We both felt that a new challenge was best for him, and I’m sure he is going to get back to his best again soon."
Cooper becomes Chesterfield’s seventh summer signing.