Last 2 years I've pulled a few in the 1st 2 weeks of June as far south as the Chagrin goes. Unfortunately I kinda abandoned the river this year really early and only fished it 2 days since beginning of May.
Last year or idk if it was year before there was sorta that drought where the late stragglers got gated off in pools end of May beginning of June.
I've caught them as late as 2nd week of June and caught them as early as 3rd week of August. But for those I put in an absolute butt-ton of hours fishing with so many skunked days to catch 'em that late and early.