Onalaska is a city in La Crosse County, Wisconsin. The 2011 Census Bureau estimates the city had a population of 18,097. It is part of the La Crosse Metropolitan Area.
Onalaska is built on a slightly elevated ridge above the Black River. Natural areas include river bottomland as well as high, heavily wooded, scenic bluffs. A manmade reservoir at the city's western edge is known as Lake Onalaska. Onalaska is known as "The Sunfish Capital of the World."
The original village (now city) was platted by Thomas G. Rowe (New York) and John C. Laird (Pennsylvania) in 1851. In its early days, lumbering and related industries served as a basis for its economy.