23 campgrounds with first-come sites in Maryland

Every one of them is run by the National Park Service. 21 of them charge nothing for a night. The biggest is Assateague Island National Seashore Campground with 160 sites.

A campground is listed when Recreation.gov or the Forest Service records it as first-come, first-served. Campgrounds where some sites book online and the rest are first-come are listed too, marked partly reservable.