From the record
“The Gerhardt Octagonal Pig House near Gladstone, North Dakota, United States, was built in 1930. It was listed on the National Register of Historic Places in 1986.”
Wikipedia article Gerhardt Octagonal Pig House, CC BY-SA 4.0.
One of 6 National Register listings published here for Stark County · category: Building.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service