Ootmarsum is a town in the Dutch province of Overijssel. It is a part of the municipality of Dinkelland, and lies about 10 km north of Oldenzaal. It received city rights in 1325. Ootmarsum was a separate municipality until 2001, when it became a part of Dinkelland. In 2001, the town of Ootmarsum had 4227 inhabitants. The built-up area of the town was 1.5 km², and contained 1620 residences. The statistical area "Ootmarsum", which also can include the peripheral parts of the town, as well as the surrounding countryside, has a population of around 3650.