Black River Falls, WI has a population of 3,566 and is the 7,961st largest city in the United States. The population density is 865 per sq mi which is 890% higher than the Wisconsin average and 855% higher than the national average. The median age in Black River Falls is 43 which is approximately 10% higher than the Wisconsin average of 39. In Black River Falls, 56% of the population over 15 years of age are married, 96% speak English and 1% speak Spanish. 77% of Black River Falls residents were born in Wisconsin, 21% were born out of state, 0% were born outside of the United States and 1% were foreign born.