Not all plazas have them one that does is around Portage before Cleveland and the other is in Amherst about 30 miles after Cleveland. There is a $20 fee for a spot there with hookups. On the west side there are a few Walmarts one in North Olmsted then Avon and finally in Elyria. all are open 24 hours and in nice areas. If you are on I-90 there is a rest area but I don't think they allow overnight stays and I don't think I would stay there anyway.
Outside of the parking lot boondocking I don't know of any true boondocking place. There is a lot of farm land west of Cleveland heading south of the Ohio Turnpike but all private land.