Allegany County is located in the Southern Tier region of New York state. Allegany County has a total area of approximately 1034 square miles of which 99% is land and and less than 1% water. As of the census of 2000, there were 49,927 people, 18,009 households, and 12,192 families residing in Allegany County, New York. Out of the state's 58 counties, it ranks as 45th most populous. Pennsylvania is on Allegany county's southern border. ts name derives from a Delaware Indian word, applied by settlers of Western New York State to a trail that followed the Allegany River.