The John Messer Barn is a historic structure within the Great Smoky Mountains National Park in Sevier County, Tennessee, United States. Located along the Porters Creek Trail in the Greenbrier valley, it was constructed in 1875 by Pinkney Whaley. The Whaleys later sold their farm to John H. Messer, who was married to Pinkney's cousin, Lucy. In the 1930s, the Smoky Mountain Hiking Club, which constructed the Smoky Mountain Hiking Club Cabin nearby, leased the barn from the National Park Service.
The barn was added to the National Register of Historic Places in 1976, and is the last surviving structure from the pre-park Greenbrier Cove community. This barn should not be confused with the Messer Barn in Cataloochee, which was built by John's cousin, Will Messer.