Until 1982, the parishes that now make up the Idukki diocese belonged to the Diocese of Kottayam. That year, the churches in the eastern part of Kottayam diocese were separated to form Idukki as its own diocese.
Counts above reflect Orthodox-held institutions only; churches, chapels, and other properties currently under schismatic occupation are catalogued separately below and are not included in these totals.
4 districts, listed alphabetically.