ILMENAU, a town and summer resort of Germany, in the Land of Thuringia, at the north of the Thuringian Forest, on the river Ilm, 3o m. by rail south of Erfurt. Pop. Formerly a part of the county of Henneberg, Ilmenau came in 1631 into the possession of electoral Saxony, afterwards passing to Saxe-Weimar. It was a favourite resort of Goethe, who wrote here his 1 phigenie. It manufactures glass, porcelain, toys, chemi cals, surgical instruments and turnery.