Erie is a city in, and the county seat of, Neosho County, Kansas, United States, and situated in the valley of the Neosho River, approximately …Erie is a city in, and the county seat of, Neosho County, Kansas, United States, and situated in the valley of the Neosho River, approximately one mile northeast of the river. As of the 2020 census, the population of the city was 1,047.