Illmitz is a market town in the district of Neusiedl am See in Burgenland in Austria. It is located in a region to the east of the Lake Neusiedl which is named the Seewinkel.

The town is at an elevation of 117 meters above sea level. Nearby, an area 114 m (374 ft) above sea level is the lowest elevation of Austria. Characteristic of the area are wide open plains and salt marsh flora, with many small salt lakes around. The Lange Lacke (Long Lake) is the largest of about forty such lakes nearby.