Here is a map of traditional British Counties https://en.wikipedia.org/wiki/Association_of_British_Counties#/media/File:CountiesOfGreatBritain.PNGLang and Long both mean long. Lang is the older archaic form. The Most common form is now Long. The names occur in two areas, Firstly north west England including Westmorland, Cumberland and the old northern part of Lancashire all of which has been stuck together in the modern creation of Cumbria:Longstaff in 1881 census:Westmorland 92Lancashire 91 plus 21 Langstaffs and 9 LangstaffeCumberland 38The second area is the North West centred on the County Durham/Yorkshire border:Longstaff:Durham 866 plus 77 Longstaffe, 10 Longstaf, 25 Langstaff, 5 Langstaffe 4 Langstaf.Northumberland 153 plus 22 Longstaffe and 3 Longstaf.Yorkshire 442 plus 29 Longstaffe, 7 Longstaf, 234 Langstaff, and 6 LangstaffeLincolnshire 10 plus 24 LangstaffsIt is notable that the Lang variant is pretty restricted to Yorkshire and is comparatively unusual in County Durham.Elsewhere Cambridgeshire has 39 Longstaffs, Hereford 12, Hertfordshire 20 London 143 and Staffordshire 29.According to the "American Dictionary of English Family Names" Longstaff is "apparently an occupational name for a tipstaff or beadle who carried a long staff as a badge of office; perhaps also a nickname for a very tall, thin man, or even an obscene nickname for a man with a long sexual organ. The surname is found chiefly in northeastern England." Well there you have a whole series of wild guesses.Surnames will drift to known current words over a period of time and in the context of local accents. The name Langton can have the -t- modified to -st-, -th-, or replaced by -h-. With the remaining weak -on you can guess the results. The least changed are Langstone/Langston and Langthorn which all keep the -n as does Langhorn. Langstaff drops the -n completely as familiarity will complete Langst with Langstaff. We all understand what a long stone, long staff or long horn are. Once the surname has been captured it is not going to return to its original form. If the geographic name Langton is the origin of Longstaff/Langstaff we should find a Langton village where the Longstaff/Langstaff surname has its highest density.If we start with Westmorland, Cumberland, Lancashire, the highest density of Longstaff is in Warcop, Westmorland. The next village is Langton except it isn't anymore because the Scots destroyed it in 1328 burning down the church. The parish is still called Langton. Not all villages give rise to families with the village surname. However in this case we know that happened because the Langton family were famous even having an Archbishop of Canterbury Thomas Langton who died of the plague as soon as he was elected. He is most famous for saying what a good guy Richard III was. The name of junior branches would have drifted to Langstaff/Longstaff.If Longstaff in Westmorland derives from the geographic settlement Langton meaning a settlement on/by a long don(hill) is the same true of Longstaff/Langstaff in south County Durham/North Yorkshire? Is there even a Langton village there? Yes, there is Langton in County Durham in a very rural area. If that is the origin of the name we should expect to find the maximum concentration nearby. In fact that occurs in Witton-le-Wear which has the highest concentration in Durham of both Longstaff and Langstaff. It also has the highest concentration of Langthorn an almost non existent name. So Langton drifts not only to Langstaff but to Langthorn. Langthorn was not named after someone with thorn in his thumb.Langton in Durham is situated between Bishop Auckland, Barnard Castle, Richmond and Darlington. This is precisely where we find the Longstaff name in the area otherwise known as Teesdale in Durham and Richmondshire in Yorkshire. But was there ever a Langton family there? Yes, and a famous one.https://www.british-history.ac.uk/vch/durham/vol3/pp315-321http://www.lostlangtons.co.uk/DurhamLangtons.shtmlhttps://www.british-history.ac.uk/vch/durham/vol3/pp247-254So if you are a Longstaff or a Langstaff do you choose between your surname and Langton? Of course not, it is just a spelling variation, you embrace them both. But you are not descended from an unknown official of unknown office who waved a stick about, rather you are descended from one of two famous families. So we can try and work out which one please consider a FTDNA Y37 test. Thankyou.
Here is a map of traditional British Counties https://en.wikipedia.org/wiki/Association_of_British_Counties#/media/File:CountiesOfGreatBritain.PNG 



https://archive.org/details/langstaffsoftees00long/page/n9/mode/2up

A previous administrator wrote: The Langstaff name appears in many countries, Canada, USA, England and Ireland being the most common.
My family came from Ireland, County Wexford, in 1825 to Grenville County, Ontario. I have the family starting from there and only guesses at what came earlier.