St. Mary's is a small clapboard Catholic church built by the Marquis de Mores in 1884 for his wife Medora and the town's mostly French and Irish workers. White-painted timber, a steep gable, and a simple bell tower — it is one of the oldest standing churches in North Dakota.
The interior is plain but well kept, with original stained glass and pews. It is still used for services. Outside service hours the church is sometimes open to visitors; otherwise enjoy it from the outside as part of a walk through Medora's compact historic core.