I frequent the Weston Bend St park in NW Missouri thru the winter. Very peaceful, often with just a few campers and the CG host there.
This park has frost free hydrants in several places in the park that are in operation year round. The vault toilets are open, however the showerhouse that has running water and flush toilets is closed in winter. Electricity is available at the camp sites, and I have never seen the dump station closed, although I don't use it in the winter. I leave my trailer winterized, and just use the vault toilets at camp.
The nightly fee is a few dollars cheaper during the winter.