The name Armstrong derives from a Middle English nickname which meant someone with strong arms.
The Scottish Armstrong is reputed to have been originally bestowed by "an antient (sic) king of Scotland" upon "Fairbairn, his armour-bearer" following an act of strength in battle.
In Ireland the name was also adopted as an Anglicization of two Gaelic names from Ulster: Mac Thréinfhir (meaning "son of the strong man") and Ó Labhraidh Tréan (meaning "strong O'Lavery").
Although the name "Armstrong" is quite common in the Aghagallon and Glenavy area of County Antrim in Northern Ireland, the other names are to be found within the nine Ulster Counties and Scotland, especially along the west coast.
In the UK this surname is well represented in North East England, Cumbria, Lancashire, Yorkshire, Scottish Borders, Lanarkshire, Ayrshire, Dumfries & Galloway, and Northern Ireland.