This is a classic ledged-and-braced (or Z-braced) plank door, a utilitarian style common in American homes, barns, sheds, cellars, or outbuildings. Were fairly positive on the age since it came off the original homestead shack of the property we purchased. The original house was estimated to be 1875-1885 era This is only half the original door as that's how the were made back then.
As is due to age and condition, but a solid find. $250 OBO