The territory was established as the Vicariate Apostolic of Sierra Leone, on 13 April 1858 by Pope Pius IX, taking territory from the Vicariate Apostolic of Two Guineas and Senegambia.

[3] The vicariate was elevated to the status of a diocese, taking the name of Freetown and Bo on 18 April 1950.

[4] The diocese covers an area of 4,677 square kilometres (1,806 sq mi),[3] around the Sierra Leone capital city of Freetown.

[3] The archidiocese has three suffragan dioceses, those of Bo, Kenema and Makeni.

[7] Work on its construction began in November 1884 and was dedicated on October 27, 1887.