St. Illog in Hirnant has been the site of a church since the early medieval period, however there is little trace of its historic past. In 1886 the church was almost entirely dismantled and replaced, save for the north wall which retains its medieval stone construction. The nineteenth century rebuilding, by Lawrence Booth of Manchester, includes stone dressings, principals and spars for the roof, and pulpit and altar rails from the submerged church at Llanwddyn. The western end and bellcote were rebuilt once again in 1996.
St. Illog's consists of a single chamber with a west bellcote, primarily built from quarry-cut stone with yellow sandstone dressings, dating largely from the nineteenth century.
During the two renovations this church has undergone most of the early fabric and fittings of the building have been removed, but the medieval font was recently restored to its original setting.

Source: RCAHMW Inventory Documents

K Steele, RCAHMW, 14 November 2008