Four Mile Creek state park is on Lake Ontario, about 15-20 minutes north of the Falls, big campground. Some sites have electric. There are water hookup locations around the park and a dump station. Nearby is Ft. Niagara (no camping), with interesting museum and fort to tour.
If you stay there, show your hang tag to the Niagara Falls State Park parking lot attendant for free parking (versus $10 a day.) If you arrive early (by 9 am in the summer and maybe weekends off season), there are some shady parking places along the sidewalk in Lot #1.