The first historical mention of the diocese of Jīlū is from 1580, when the metropolitan of Jīlū, Siirt and Salamas, was elevated to the patriarchate of the Chaldean Catholic Church as Mār Shim'on IX Dinha (1580-1600). That year the new patriarch consecrated a metropolitan for Jīlū named Mār Sargīs, who was among the signatories of a letter from him to Pope Gregory XIII, and he is probably the same as the Metropolitan Mār Sargīs of Jīlū mentioned in hierarchies listed in the reports of 1607 and 1610 sent by Catholic patriarch Mār Shim'on X Eliyā (1600-1638) to Pope Paul V.