New York State Route 400 (NY 400) is a 16.91-mile (27.21 km) freeway located within Erie County, New York, in the United States. The northwest end is connected to the New York State Thruway and the southeast end terminates at NY 16 in the town of Aurora. NY 400, known as the Aurora Expressway, roughly parallels NY 16 between the two locations. It is most commonly used to carry traffic from Buffalo to the village of East Aurora, where Fisher-Price and Moog, Inc are headquartered. It is a busy commuter route to the southern suburbs. NY 400 is signed as a north–south route, although about half of the route runs more east–west.

Erie County is a county along the shore of Lake Erie in western New York State. As of the 2020 census, the population was 954,236. The county seat is Buffalo, which makes up about 28% of the county's population. Both the county and Lake Erie were named for the regional Iroquoian language-speaking Erie tribe of Native Americans, who lived in the area before 1654. They were later pushed out by the more powerful Iroquoian nations tribes. The county is part of the Western New York region of the state.