The town derived its name from the O’Farrell Clan. There has been a long thousand-year connection between Longford and the Farrell clan. The O'Fearghails were the Gaelic rulers of Annaly; having lost control of their territory some 400 years ago, the Clan took flight and lived abroad for some time. The majority of those that returned settled in Longford. Today the surname Farrell is still the prominent surname in the county.