The Diocese of Gary serves an estimated 170,000 Catholics in Lake, Porter, LaPorte and Starke counties, located east of Chicago, around the Indiana coastline of Lake Michigan. The diocese includes 58 parishes, two missions, one Catholic student center, 17 parish elementary schools and three diocesan high schools serving 6,259 students. An additional 5,610 students are enrolled in parish Catholic faith formation programs. The diocese is home to two post-secondary institutions. More than two million are served by Catholic-affiliated agencies, including seven Catholic hospitals, residential and daycare facilities for adults and children, and centers for Social Services.

The diocese was established on Dec. 17, 1956, when the Vatican announced that the four Northwest Indiana counties would be separated from the Diocese of Fort Wayne to form a new diocese. Since then, the faithful of the Diocese of Gary have been guided by five bishops, including the current ordinary, Bishop Robert J. McClory.

In 1986, the Northwest Indiana Catholic was established as the official diocesan news source. A small editorial staff produced the weekly newspaper until 2020, when it switched to a bi-weekly schedule to facilitate better local story development, the expansion of a broad-reaching digital news site and the creation of occasional magazines sent to every home. On March 16, 2025, the NWI Catholic distributed the last printed newspaper to nearly 4300 subscribers and elevated digital news distribution through daily posts and a weekly e-newsletter to more than 14,000 recipients.