Ilium is a fictitious town in eastern New York state, used as a setting for many of Kurt Vonnegut's novels.
The name most likely refers to Troy, New York ("Ilium" was the name the Romans gave to ancient Troy), although Troy is mentioned as a separate city in Player Piano. In all other respects, Ilium very closely resembles Schenectady, New York, with the fictional Iroquois River standing in for the real Mohawk River, which flows west-east through Schenectady. The Ilium Works is in roughly the same geographic location as the General Electric plant in Schenectady, where Vonnegut worked as a public relations writer. Still, the city of Ilium is quite clearly distinct from Schenectady, as characters in Player Piano, Cat's Cradle, and Slaughterhouse-Five refer to Schenectady as a separate place. Besides, Schenectady is in a real sense divided into three parts as in Player Piano: Schenectady proper, Scotia across the Mohawk River, and Niskayuna.
Cohoes, longtime residence of Vonnegut's character Kilgore Trout, is in the vicinity of Ilium, and of the real towns that inspired it.
In Vonnegut's Galápagos, Mary Hepburn was a High School teacher in Ilium, and in Cat's Cradle, it is the former home of Dr. Felix Hoenikker—one of the fathers of the atomic bomb—thus, it is the town that John visits to interview Dr. Asa Breed, Hoenikker's former supervisor. In Player Piano, it is where most of the action takes place. In Slaughterhouse-Five, it is also the home town of the book's primary protagonist, Billy Pilgrim. Ilium is also where the events of the short story "Ed Luby's Key Club"(from "Look at the Birdie") take place.