Marengo is a town in Ashland County in the U.S. state of Wisconsin. The population was 390 at the 2010 census.
Marengo is located in northwest Ashland County, south of the town of White River, west of the towns of Ashland and Morse, and north of the town of Gordon. To the west are the towns of Grandview and Lincoln in Bayfield County. The Brunsweiler River, a tributary of the Marengo River and thence the Bad River, flows south to north through the town, passing through several small lakes.
According to the United States Census Bureau, the town has a total area of 72.4 square miles (187.6 km2), of which 71.5 square miles (185.2 km2) is land and 0.93 square miles (2.4 km2), or 1.26%, is water.
As of the census of 2000, there were 362 people, 132 households, and 99 families residing in the town. The population density was 5.1 people per square mile (2.0/km2). There were 191 housing units at an average density of 2.7 per square mile (1.0/km2). The racial makeup of the town was 96.96% White, 2.49% Native American, 0.28% Asian and 0.28% Pacific Islander. Hispanic or Latino of any race were 0.28% of the population. 32.5% were of Finnish, 23.8% German, 6.5% Swedish, 5.9% United States or American, and 5.6% Norwegian ancestry according to Census 2000.