Call Calvert County Department of Parks and Recreation during their business hours.
Apparently you can because we just tried to go to the publicly funded park with our kids and were told that the entire playground was reserved for a therapeutic center event and that we'd have to come back when it was over.... so, you can claim public property and deny the public access to it at Hallowing Point park.
You can't rent the public park for yourself but you can have an event and let the public come, but you can't stop people from coming.
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