Hi
There certainly was a barracks in Weeley during the Napleonic War and slightly later - dates appear to be around from at least 1803 until possibly as late as 1820. The barracks were then dismantled.
http://www.uk-genealogy.org.uk/england/Essex/towns/Weeley.htmlThe British Army moved battalions around the country and in barracks and garrisons abroad regularly so you could find many regiments stationed in any barracks including Weeley. The battalions were not necessarily associated with the area they were stationed at though each regiment had a smaller depot which was somewhere in their county of origin. Most regiments usually only had one battalion rising to two during periods of war like the Napleonic period (or more during the First World War). If a regiment maintained a second battalion (from which soldiers were used to supply the first which would be serving abroad) later on in the C19th, then that battalion was often stationed at the regimental depot which might be large enough to be a garrison (more than one barracks) in which case other regiments would often be stationed with them.
'Because of fears that a standing army in barracks would be a threat to the constitution, barracks were not built in Great Britain until 1790, on the eve of the Napoleonic War.'
'The regimental depot of a regiment is the regimental headquarters and normally also the place where recruits are assembled and trained. It is also where soldiers and officers awaiting discharge or postings are based, and where injured soldiers return to full fitness after discharge from hospital before returning to full duty. A variety of regimental stores will also be kept at the depot.'
Examples of regiments stationed at Weeley Barracks
Queens Own Highlanders
(Seaforth & Camerons)
1808
'The embarkation was effected in safety, and on the army arriving in England in February, the 79th marched to Weeley Barracks, in Essex, about 10 miles from Chelmsford, where many of the men were shortly afterwards attacked with fever, though not a man died.'
42d Royal Highland Regiment
(The Black Watch)
'They remained in their new quarters, giving way too freely to the temptations to which they were exposed, by the hospitality of the inhabitants, till the spring of 1803, when, in consequence of the interruption of peace, they were embarked at Leith for the camp then forming at Weeley, in Essex.'
The Essex Regiment was formed in 1881 following the union of the 44th (East Essex) Regiment of Foot and the 56th (West Essex) Regiment of Foot. I don't know where the regimental depots were for these two regiments during the Napleonic War but Rootschat Armed Forces board experts will probably be able to tell you and give you more information on Weeley Barracks. The battalions themselves were stationed in many places throughout the British Empire during the C19th.
Regards
Valda