People tend to check in during these times:
Be ready to pay $7 to see it, but well worth it as a historical site! Plenty of hiking trails and the people working are informative and nice
I recommend going to the National Park in Chillicothe, Ohio over the Serpent Mound. It costs $7 to park, but if you bypass museum and go straight to mounds, you can get away with it. Not worth it!
Hike on the trail that goes under the ledge of the earthworks!