Marietta is a city in Lac qui Parle County, Minnesota, United States on Minnesota State Highway 40 near the South Dakota border. The population was 162 at the 2010 census.
According to the United States Census Bureau, the city has a total area of 0.4 square miles (1.0 km²), all of it land.
As of the census of 2000, there were 174 people, 86 households, and 47 families residing in the city. The population density was 445.2 people per square mile (172.3/km²). There were 109 housing units at an average density of 278.9 per square mile (107.9/km²). The racial makeup of the city was 100.00% White.