West of the train line industry companies settled, the number of inhabitants rose from 1,000 in the year 1800 to 2,500 in the year 1930. From the 1923 inflation the market municipality recovered in 1926. Then came the Nazi regime and the World War II, a time of fall. Three years after the war the currency reorganization and the free-market economy led in an upswing like never before. New production branches settled. Thus Illertissen could switch itself into the industrializing without destroying the natural living room, the social equilibrium or the skyline. In addition also the refugees of homeland made a remarkable contribution. Straight the 1971 integrated quarter Betlinshausen as well as 1978 in the framework of the local regional reorganization been added quarters Au, Jedesheim and Tiefenbach round the picture off to a grown whole one. Therefore Illertissen was made to a town with around 16,000 inhabitants. In the case of the district reorganization the former district capital Illertissen had to deliver some offices to the district of Neu-Ulm, but Illertissen did not lose its economical meaning as a regional middle center in the south district. Illertissen is served by the Neu-Ulm-Kempten railway.