Blair is a city in Trempealeau County, Wisconsin, along the Trempealeau River. The population was 1,325 at the 2020 census. Blair is on the f…Blair is a city in Trempealeau County, Wisconsin, along the Trempealeau River. The population was 1,325 at the 2020 census. Blair is on the former Green Bay and Western Railroad, which ran down the Trempealeau River valley to Winona, Minnesota.