Agnes Longmore born about 1450 of "Mere Manor, Whittington, Staffordshire, England" is the earliest on record at the FamilySearch website.
Whilst it is tempting to believe that several groups of Longmores all originated simultaneously on various long moors around the UK countryside, it is a little more complex than that. One person who did a well-researched one name study of the Longmire surname said the vast majority of Longmores can be traced back to Cumberland. There is plenty of evidence to suggest that the Longmores originated in the Lowlands of Scotland in the region of Ayr and didn't begin to disperse until around 1300 - the time of King Edward I. Certainly you can link the Longmores in the South Shields to those in Staffordshire just by taking a look at the Victorian censuses on the "The Longmore Pages". Similarly, those in the Southampton area (such as Sir Thomas Longmore, the Surgeon-General at the time of the Crimean War) can be linked to the other high-ranking military men, surgeons and lawyers amongst the Hertfordshire Longmores. There is also plenty of recent evidence of how the Longmores dispersed within England. You have to go back to the early pipe rolls and scrolls to discover evidence linking the Scottish Longmores to those in England and there is also evidence available of how Longmores migrated from Scotland to Ireland many years ago. Of one thing we can be sure, the Longmores in the USA, Canada, Australia and New Zealand all originated from either England, Scotland or Ireland - there was even a Longmore on the Mayflower. This surname originates from several places. The list of places below is from a quick extraction from search results of the FamilySearch website.
To see the distribution of Longmores in the UK go to Surname Profiler
Longmore related websites