Irondequoit Bay is a large body of water located in northeastern Monroe County, New York. The bay, roughly 0.5 miles (0.80 km) wide and 4 miles (6.4 km) in length, is fed by Irondequoit Creek to the south and flows into Lake Ontario at its northern end. On average, the surface of Irondequoit Bay rests at 245 feet (75 m) above sea level and is 80 feet (24 m) deep at its deepest point a short distance north of the Irondequoit Bay Bridge carrying the six-lane New York State Route 104 over the bay.
The center of the bay acts as the eastern border for the town of Irondequoit and the western border of the towns of Penfield and Webster. The Irondequoit–Penfield boundary continues along the center of Irondequoit Creek south of the New York State Route 404 (Empire BLVD) float bridge.