The La Crosse River is a 61.3-mile-long tributary of the Mississippi River in southwestern Wisconsin in the United States. The La Crosse River rises in northern Monroe County and flows generally west-southwestwardly into La Crosse County, through the Fort McCoy military installation and past Sparta, Rockland, Bangor and West Salem. It flows into the Mississip…The La Crosse River is a 61.3-mile-long tributary of the Mississippi River in southwestern Wisconsin in the United States. The La Crosse River rises in northern Monroe County and flows generally west-southwestwardly into La Crosse County, through the Fort McCoy military installation and past Sparta, Rockland, Bangor and West Salem. It flows into the Mississippi River at the city of La Crosse.