According to the Mattoon Gazette, 2-8-1878, a soldier from Co. D, 126th IL says Camp Terry was "an old fair ground," about a mile from Mattoon, and that the 21st IL had been organized there. By the time of the 126th the camp had barracks and was enclosed by a fence.
Same 8-29-1913 says the 79th was organized at Camp Terry in August 1862.
So it appears Camp Grant and Camp Terry were two names for the same encampment.