Allegany is an unincorporated community in Coos County, Oregon, United States east of Coos Bay. According to Oregon Geographic Names, a post office was established there in 1893, and it is unknown why this spelling was chosen rather than the more common form, Allegheny, used for many features in the eastern United States. (The "Allegany" spelling is most common in the state of New York, suggesting the Oregon town's founders were from that area; in contrast, the "Allegheny" spelling is used primarily in Pennsylvania.)
The East Fork Millicoma River and West Fork Millicoma River join at Allegany to form the Millicoma River, a short tributary of the Coos River. The Golden and Silver Falls State Natural Area is a state park northeast of Allegany.