The province of Ilorin can be linked to the old western region of Nigeria which was mainly evangelized by the Society of African Mission (SMA), We have the accounts of the five earliest contacts with the catholic faith through western Nigeria from separate locations as follows: Offa 1912, Oro 1918, Eruku 1918, Aare-Opin 1918 and Ayedun, former Aye-Ekan 1912. By 1943, the entire province of Ilorin, which used to be part of the vicariate of the Bight of Benin (Lagos) was removed and formed part of the Vicariate of Ondo-Ilorin. And by 1950 the whole area became the diocese of Ondo. With the independence of Nigeria in 1960, it was desirable that church jurisdictions should not cross the region boundaries; this necessitated the creation of separate prefecture Apostolic in January 20, 1960 aclled independent Ecclesiastical jurisdiction of Ilorin. By December 6 1961 Rev. Fr. William Mahony was appointed prefect Apostolic of Ilorin. Later it was raised to th status of a diocese with Rt. Rev (Dr) William Mahony (SMA) as its first Bishop.
The great task of building up the diocese of Ilorin began in earnest inn 1969 with the inception of the diocese pastoral exercises commenced. Subsequently parishes were created and Ilorin became the centre of all pastoral and administrative apostolate. Further developments were witnessed in the areas of education and health facilities.
Bishop William Mahony SMA was succeeded by his auxiliary Bishop the Rt. Revd. (Dr) John Olorunfemi Onaiyekan, the first indigenous Bishop of the diocese of Ilorin on the 6th January 1985. On the 17th of May 1992, Most Revd. Dr Ayo Maria Atoyebi OP was installed the third Bishop of the diocese, succeeding Most Revd John Onaiyekan who was appointed the Archbishop of Abuja Archdiocese.
From the very few parishes, the diocese which now covers the whole of the present Kwara State, now has 30 parishes including Quasi Parishes and Chaplaincies
First Mass in the Diocese 1912
First Missionary Rev. Fr. I. Ekins
First Bishop Most Rev. W. Mahony SMA
Second Bishop Most Rev. John Onaiyekan
Third (Current) Bishop Most Rev. Ayo-Maria Atoyebi OP
Patron of the diocese: St. Joseph, the Husband of Blessed Virgin Mary