The Diocese of Biloxi is a Latin Church ecclesiastical territory, or diocese, of the Catholic Church that encompasses 17 counties in southern Mississippi in the United States. The diocese was erected on March 1, 1977, when it was split from the Diocese of Jackson. The Diocese of Biloxi is a suffragan diocese of the ecclesiastical province of the metropolitan Archdiocese of Mobile, though for its first three years the diocese was in the province of the Archdiocese of New Orleans.

The Diocese of Jackson is a Latin Church diocese in Mississippi in the United States. Its ecclesiastical jurisdiction includes the northern and central parts of the state, an area of 97,458 square kilometers (37,629 sq mi). It is the largest diocese, by area, east of the Mississippi River.