Rochester is a city in the U.S. state of New York, the seat of Monroe County, and the fourth-most populous in the state after New York City, Buffalo, and Yonkers with a population of 211,328 in 2020. The city of Rochester forms the core of a larger metropolitan area with a population of 1 million people, across six counties, which in turn is part of the larger Western New York region that has a population of roughly 2.5 million.