From territorial days, all able-bodied men in Missouri aged 18-44 provided mandatory service in the Missouri State Militia. Newly-arrived settlers were exempt from service for three months after arrival. Congress stipulated the organization and function of state militias in detail, including requirements for uniform structure, training, and functioning. The state spelled out further details as enacted by the General Assembly.
The state constitution of 1820 mandated that rank and file militia members elected field officers and company officers, field officers in turn elected brigadiers general, and the brigadiers and field officers elected majors general. General and field officers appointed officers of their staffs. At the state level, the governor appointed an adjutant general.
Militia battalions regularly drilled, although the regularity and quality of the drill likely varied. Certain days, days of elections being one, were set aside as days when militia drill could not occur. Officers posted calls for muster and drilling in public places, and printed them in local newspapers. Members avoiding drill were subject to fines.
The law required newly inducted militia members to assemble their own equipment within six months. Items had to provide a good musket or firelock, a sufficient bayonet and belt, two spare flints and a knapsack, a pouch with an ammunition box containing at least 24 cartridges suitable to their firearm. Alternatively, recruits could provide a good rifle, knapsack, shot pouch and powder horn, 20 balls appropriate for their rifle, and ¼ pound of powder. The men had to bring all items to exercise or service. Although the militia formally prepared, the governor called up the militia on relatively few occasions for some years after statehood.