The Diocese of Columbus (Latin: Dioecesis Columbensis) is a diocese of the Catholic Church covering 23 counties in central Ohio in the United States. It is a suffragan diocese in the ecclesiastical province of the metropolitan Archdiocese of Cincinnati. The mother church is St. Joseph Cathedral in Columbus. The diocese was erected in 1868. The current bishop is Earl K. Fernandes.

The Diocese of Columbus contains 108 parishes in 23 counties:

Coshocton, Delaware, Fairfield, Fayette, Franklin, Hardin, Hocking, Holmes, Jackson, Knox, Licking, Madison, Marion, Morrow, Muskingum, Perry, Pickaway, Pike, Ross, Scioto, Tuscarawas, Union, and Vinton.

During the 17th century, present-day Ohio was part of the French colony of New France. The Diocese of Quebec had jurisdiction over the region. However, unlike other parts of the future American Midwest, there were no attempts to found Catholic missions in Ohio.

In 1763, Ohio Country became part of the British Province of Quebec, forbidden from settlement by American colonists. After the American Revolution ended in 1783, Pope Pius VI erected in 1784 the Prefecture Apostolic of the United States, encompassing the entire territory of the new nation. In 1787, the Ohio area became part of the Northwest Territory of the United States. Pius VI created the Diocese of Baltimore, the first diocese in the United States, to replace the prefecture apostolic in 1789.

In 1808, Pope Pius VII erected the Diocese of Bardstown in Kentucky, with jurisdiction over the new state of Ohio along with the other midwest states. Dominican priests from Bardstown were the first missionaries and clergy in the Columbus area. The first Catholic chapel built in Ohio was a log structure in Perry County; it was dedicated in 1818 by Edward Fenwick.

Pope Pius VII in 1821 erected the Diocese of Cincinnati, taking all of Ohio from Bardstown. The visit of Cincinnati Bishop John Purcell to central Ohio in June 1836, began the activity of the Catholic Church in the city of Columbus. After saying Mass in a house on Canal Street on June 5, Purcell asked the Catholic men in attendance to meet regarding the construction of a church. They developed a plan to build a church on a lot already owned by the Catholics of the area—where Holy Cross Church now stands. In 1837, the diocese sent a resident pastor, Henry Juncker, to cover the Columbus and Chillicothe areas. Juncker built Holy Cross Church, opening it in 1838 with a Sung Mass. By 1843, Holy Cross parish was scheduling multiple masses on Sundays and building a school.

At the close of the Second Plenary Council of Baltimore in 1866, the American bishops petitioned Pope Pius IX to establish a new diocese with its seat in Columbus. On March 3, 1868, the pope erected the Diocese of Columbus, encompassing the portions of Ohio "...lying south of 40' and 41" and between the Ohio River on the East and the Scioto River on the West together with the Counties of Franklin, Delaware and Morrow." Auxiliary Bishop Sylvester Rosecrans of Cincinnati was made the first bishop of Columbus.