尼亚加拉县（Niagara County, New York）是美国纽约州西部的一个县，成立于1808年。北傍安大略湖，西邻加拿大。面积2,952平方公里。根据美国2000年人口普查，共有人口219,846。县治洛克波特市。

县名来自中立印第安语的onghiar，意思是「水的雷鸣」，指的就是著名的尼亚加拉瀑布。

Niagara County is a county located in the U.S. state of New York. As of the 2010 census, the population was 216,469. The county seat is Lockport. The county name is from the Iroquois word Onguiaahra; meaning the strait or thunder of waters.\

Niagara County is part of the Buffalo-Niagara Falls metropolitan area, and its Canadian border is the province of Ontario.