The Irish, Welsh and Cornish surname Glynn is a topographic name for someone who lived in a valley, Welsh glyn, Cornish glin, or a habitational name from a place named with this word. When found in Ireland it is a reduced form of the Gaelic name Mag Fhloinn, anglicized as McGlynn. The main sept of the clan "Mag Fhloinn" originated in the area of County Westmeath and County Roscommon from where they spread west of the River Shannon, mainly to County Sligo, and north to Donegal. The first recorded spelling of the family name is shown to be that of James Glynn, which was dated 1617, a grand juror of County Tipperary, Ireland. There are approximately 9,000 bearers of the name in the United States today.