Neptune is an unincorporated community in Mercer County, in the U.S. state of Ohio.[1]
Neptune was laid out in 1837.[2] A post office was established at Neptune in 1839, and remained in operation until 1905.[3]
40°36′11″N 84°29′30″W / 40.60306°N 84.49167°W / 40.60306; -84.49167