Jennings
Jennings—This name is the anglicised form of Keoneen and O'Keoneen in the districts surrounding Tuam, Co. Galway, and in the most parts of Co. Sligo, in Gaelic Mac Sheóinín. The name means "Son of Little John," and is of Anglo-Norman origin.
Alphabetical Index of Anglicised Surnames in Ireland
See also Woulfe’s Irish Names and Surnames
… and O'Hart's Irish Pedigrees