Оновілль: Тарихы, географиясы және демографиясы

If Onoville had ever been assigned a ZIP Code, it would have likely been 14764, as gaps in the United States Postal Service's online database have ZIP codes 14761 to 14764 missing, with a town name somewhere alphabetically between Olean and Oramel; as Olean is substantially larger and ZIP Codes 14761 through 14763 were likely reserved for it but never used, it is unknown whether 14764 was reserved for Olean or Onoville). If the ZIP Code had been assigned, it likely was never used, since by the time ZIP Codes were rolled out outside the cities in 1963, the Kinzua Dam was already being built. The Onoville post office closed June 30, 1964.

According to the United States Census Bureau, the town has a total area of , of which is land and , or 0.67%, is water. The southern town line is the border of Pennsylvania and the western town line is the border of Chautauqua County. The Allegheny Reservoir cuts through the town. The South Valley State Forest occupies much of the town's area.

The south town line is the border of the townships of Pine Grove, Elk, and Mead in Warren County, Pennsylvania, and Corydon Township in McKean County, Pennsylvania. The west town line is the border of the town of Carroll in Chautauqua County, New York. To the east is the Allegany Reservation and the town of Coldspring. North of South Valley is the town of Randolph.

New York State Route 950A (West Bank Perimeter Road) is the primary road through South Valley and leads to I 86 and NY 394 to the northeast and Pennsylvania to the southwest. County Road 33 (Bone Run Road) connects NY 950A to U. S. Route 62 in Carroll. County Road 89 (Sawmill Run Road) connects to NY 950A in the former community of Onoville and leads directly to US 62 in Frewsburg.

As of the census of 2000, there were 302 people, 126 households, and 89 families residing in the town. The population density was 8.2 people per square mile (3.2/km2). There were 320 housing units at an average density of 8.7 per square mile (3.3/km2). The racial makeup of the town was 98.01% White, 0.33% African American, 1.32% Native American and 0.33% Asian. There were 126 households, out of which 22.2% had children under the age of 18 living with them, 58.7% were married couples living together, 5.6% had a female householder with no husband present, and 28.6% were non families. 25.4% of all households were made up of individuals, and 10.3% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.83. In the town, the population was spread out, with 20.5% under the age of 18, 4.3% from 18 to 24, 25.5% from 25 to 44, 34.8% from 45 to 64, and 14.9% who were 65 years of age or older. The median age was 44 years. For every 100 females, there were 125.4 males. For every 100 females age 18 and over, there were 122.2 males. The median income for a household in the town was $38,750, and the median income for a family was $47,188. Males had a median income of $32,188 versus $22,188 for females. The per capita income for the town was $20,541. About 3.8% of families and 6.4% of the population were below the poverty line, including 15.0% of those under the age of eighteen and 10.5% of those 65 or over.

Allegany Reservation – A reservation of the Seneca Nation that forms part of the east border of the town, along the reservoir. Allegheny Reservoir – The reservoir forms a lake in the southeast and cuts off part of the town. Highbanks – A campground and resettlement area run by the Seneca Nation Allegany Reservation. Onoville Marina – A marina located at the mouth of Sawmill Run at the location of a former community in the town. Sawmill Run – A stream that flows eastward into the Allegheny Reservoir, formed by the junction of its North Branch and South Branch (Gurnsey Hollow) near County Road 89. The town government offices are located near this junction.

A few scattered businesses operate in the town, including two prominent restaurants, the Horseshoe Inn on West Bank Perimeter Road and the Nic L Inn on Bone Run Road. Some small convenience stores and boating supply shops operate near the marina.