The system started out Gary & Interurban Railway Company, a subsidiary of the Chicago – New York Electric Air Line Railroad.

By that point, Insull held a virtual monopoly over electrically powered public transit throughout northern Illinois, north Indiana and southwest Wisconsin.

[2] At that point, Gary Public Transportation Company became the operator of the newly created Hammond Transit System.

It was forced to cede the service to Hammond Yellow Coach Lines after a judge determined that the company could not operate a system outside Gary city limits.

Gary Metro Center serves as the system's primary hub - it also doubles as a South Shore Line station, connecting riders to destinations in Chicago and Northern Indiana.

GPTC defines local routes as those bus lines completely within the corporate boundaries of the City of Gary.

By 2005, GPTC served five other communities with three regional routes, providing transit to Crown Point, East Chicago, Hammond, Hobart and Merrillville.