The Hession surname is predominantly found in these counties in the Census of Ireland, 1911.
Áed Ua hOissín was the name of two Irish clerics in the 11th and 12th centuries - the coarb of St. Jarlath (1050) and the first Archbishop of Tuam (1152) respectively.
[2] George Petrie who unearthed the High cross at Tuam which bears an inscription Áed Ua hOissín wrote that he was assisted by a gentleman of the name O'Heshin who little realised he was digging up the relic of an ancestor.
Darby O'Hession (spelt O'Hoysshynne) is the name of a Galway Cleric in the 16th, a vicar choral recorded in that churches first charter of St. Nicholas' Collegiate Church in Galway in 1551.
MacLysaght suggests a connection with the surname Ussher - which is probably the name of a separate and distinct family of English Origin based in Dublin and later in Galway.