No. In general it is not safe to assume that a man served with his local regiment, although of course a great many did.
It seems curious to many people as to why their soldier was not serving with a local regiment. Why was a Scotsman in the Londons? Why was a Geordie in the Devonshires? How did a lad from Surrey end up in the Argyll & Sutherland Highlanders? This article offers some clues.
Pre-war
Infantry regiments, despite their local-sounding titles, recruiting widely when looking for soldiers to join the regular army. They would operate local recruitment centres, and a man could also go to the regimental HQ or depot to enlist, but they also had representation at other recruiting centres around the country. Some regiments recruited heavily in areas you might not expect: for example the Royal Welsh Fusiliers had a very strong contingent from Birmingham and were sometimes known as the Brummie Fusiliers.
On the other hand, their recruitment for the units of the Territorial Force, a form of part-time soldiering in peace time, were almost exclusively localised. It would be very unusual to find a man in a TF unit who did not live in the local catchment.
1914-1916
The pattern continued once war began. Men joining as volunteers had a choice of regiment and although many did join their local one, the stories of men who did not – and for all sorts of reasons – are legion. Men chose a regiment because they liked its badge, or its uniform, or its reputation. Men rejected by one regiment (or turned away because of the sheer numbers enlisting in 1914) might travel to join another. Men could be influenced by a charming or bullying recruitment staff: “join the East Lancashires, lad, it’s a fine regiment”: this to a boy from Norfolk.
The Territorials continued to recruit locally.
In 1914 a new phenomenon began: the locally-raised “pals” battalions. These new units recruited strongly in a local area but detailed analyses have showed that even in these there was a proportion of men who had travelled specifically to enlist, or in some other way found their way to the unit.
Transfers
If a man left his unit after wound, sickness or injury, there was no guarantee that he would be posted back to his original unit or regiment. This became increasingly the case as the war went on. So if he had joined his local unit, he may be with a totally different one by war’s end.
Enlistment from 1916 onward
The pattern of recruitment changed drastically after the introduction of the Military Service Act brought conscription in from March 1916. To cope with the influx of larger numbers the army reorganised its training structure.
Conscripts had no choice of regiment. Once the structure was reorganised in September 1916 they went into a Training Reserve pool and from there were alotted to any regiment that needed men. The link between where a man came from and his local regiment was increasingly broken.
Summary
There is nothing unusual about a man from Wales being in the Suffolk Regiment, or a Glaswegian being in the Sherwood Foresters. Particularly for men conscripted, it was almost a norm for them not to be in a local unit.
If you do not know your soldier’s regiment, it is not a safe assumption that he joined his local regiment. Worth a try, but don’t bank on it.