A militia is an organized group of armed citizens who are authorized to defend a community. The militias of Great Britain's American colonies were almost as old as the colonies themselves. They were each community's first line of defense against riots, invasions, and attacks by Native Americans.

A colonial town's militia generally included all the white males between ages 16 and 60 from families that owned property. Some militia members were better soldiers than others. As early as 1645 a Massachusetts militia made an effort to single out its bravest and strongest men. These men—about one third of the total—were told that they should always be ready to fight at half an hour's notice. Such special groups played an important role in defending the colonies against attack during the French and Indian War of the 1750s and 1760s.

In 1774, as the American colonists prepared for war with Britain, Worcester County, Massachusetts, reorganized its militia. About one third of the best militia members were told to be ready to fight at a minute's warning. They were the first militiamen to be called minutemen. The idea quickly spread, and counties all over Massachusetts formed minutemen units.

When Paul Revere made his famous ride through the Massachusetts countryside on April 18, 1775, the minutemen responded to his warning that British troops were coming. The next morning, the minutemen in the towns of Lexington and Concord were ready and waiting. When the British troops attacked, the minutemen returned fire and forced the British to flee. The American Revolution had begun. As the war continued, minutemen units were established in other colonies, including Maryland, New Hampshire, and Connecticut.