Ontario, WI has a population of 475 and is the 19,846th largest city in the United States. The population density is 473 per sq mi which is 441% higher than the Wisconsin average and 422% higher than the national average. The median age in Ontario is 39 which is approximately 1% lower than the Wisconsin average of 39. In Ontario, 63% of the population over 15 years of age are married, 78% speak English and 22% speak Spanish. 75% of Ontario residents were born in Wisconsin, 19% were born out of state, 0% were born outside of the United States and 6% were foreign born.