The Militia were the forerunners of todays Territorial Army...
Here is the timeline for them...
1833. 48th, or Northampton and Rutland Militia
1874. reorganised as two bns: 1st Battalion, 48th, or Northampton and Rutland Militia
2nd Battalion, 48th, or Northampton and Rutland Militia
1881 3rd Battalion, The Northamptonshire Regiment
HQ at Northampton
4th Battalion, The Northamptonshire Regiment
HQ at Northampton
1899. 3rd Battalion, The Northamptonshire Regiment
formed by amalgamation of 3rd Bn and 4th Bn
1908. transferred to Special Reserve at formation of Territorial Force
1921 Special Reserve ,redesignated Militia
1924 Transferred to Supplementary Reserve
1953 Disbanded
The oldest of the auxiliary forces was the Militia which first appeared in the statute books in 1558, but traced something of a legislative continuity back to the Anglo-Saxon fyrd as constituted by King Alfred in the 9th century. Some modern militia regiments traced their corporate ancestry to the 12th century. The Militia had a formal statutory existence from 1558 to 1604, 1648 to 1735, 1757 to 1831, and from 1852 to 1908. The term "trained bands" was used to describe the more elite militia from 1573 to 1663, and continued to be used to describe the militia of London until 1793.
The Militia have always been a "territorial" force (not to be confused with the "Territorial Force"), answering to the county High Sheriff and later the Lord Lieutenant. Officers' qualifications included the provision that they be local land owners. Service in the Militia was usually voluntary, but where recruitment failed the ranks could be filled by ballot. Many classes were exempt from service in the Militia, including peers, soldiers, clergy, etc. An Act of 1662 formed the basis for Militia law until 1908.
A series of further Militia Acts, notably in 1761, 1768 and 1802 had the effect of transforming the Militia from a local police and and national defence force into a reserve for the Regular Army. Those earlier functions were now filled by the Volunteers. Between 1808 and 1812 another series of Acts made Militia service compulsory for men between the ages of 18 and 30. In the 1850s, almost every Militia regiment was mobilised for home defence in order to release the whole Regular Army to cope with the Crimean War and the Indian Mutiny.
In 1881 Militia battalions were redesignated as the 3rd (and sometimes 4th) Battalion of regular infantry regiments, but without changing their Militia status. (In the case of Ireland, ten regiments had to accommodate thirty-two battalions of militia, giving regiments up to four militia battalions.) In 1908 the Militia ceased to exist, and its units were transferred to the Special Reserve, but they retained their battalion designations in the regimental system. The Special Reserve was renamed the "Militia" in 1921, but all its units quietly went into suspended animation. Militia battalions were last embodied in the First World War, when they served to provide drafts for their regular counterparts. The Militia was not reactivated during the Second World War, and it was formally disbanded in 1953.
The late 1960s witnessed the first use of the "3rd Battalion" designator for non-Militia units. Two old Militia units survive in the 1990s: (1) The Royal Monmouthshire Militia, raised in 1539 and converted to engineers in 1877, transferred to the Territorial Army in 1953 where it has the honoured position of senior unit since the Militia took precedence over the Volunteers; (2) The Royal Militia of the Island of Jersey (which dates from the 13th century, but cannot claim seniority due to its broken history), was embodied in 1939 and became the 11th Battalion of The Hampshire Regiment. Disbanded in 1946, it was reactivated in 1987 as Jersey Field Squadron (The Royal Militia Island of Jersey) in 111 Engineer Regiment.