The militia of the various states and of the United States observe various birthdays but nayionally it may best be observed on May 4 each year. This is the anniversary of the formation of the militia concurrently with the establishment of the first permanent English colony in the later United States of America. In 1604, the Virginia Company of London established Jamestown as "James Fort" on May 4, 1607 and considered permanent after brief abandonment in 1610. All able-bodied adult males of the colony were considered members of the militia. The term militia in the United States has been defined and modified by Congress several times throughout U.S. history. As a result, the meaning of "the militia" is complex and has transformed over time. It has historically been used to describe all able-bodied men who are not members of the Uniformed Armed Services. From the U.S. Constitution, Article II (The Executive branch), Sec. 2, Clause 1: "The President shall be the Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States when called into the actual service of the United States."
Today, the term militia is used to describe a number of groups within the United States. Primarily, these are:
The organized or "select" militia defined by the Militia Act of 1903 consists of State militia forces, notably the National Guard and the Naval Militia. The National Guard, however, is not to be confused with the National Guard of the United States, which is a federally recognized reserve military force, although the two are linked.
The reserve militia are part of the unorganized militia defined by the Militia Act of 1903 as consisting of every able-bodied man of at least 17 and under 45 years of age who is not a member of the National Guard or Naval Militia.
Former male members of the armed forces are also considered part of the "unorganized militia" per Sec 313 Title 32 of the US Code until age 65.