The American Legion was chartered by Congress in 1919 as a patriotic veterans organization. Focusing on service to veterans, servicemembers and communities, the Legion evolved from a group of war-weary veterans of World War I into one of the most influential nonprofit groups in the United States. Membership swiftly grew to over 1 million, and local posts sprang up across the country. Today, membership stands at over 2.4 million in 14,000 posts worldwide. The posts are organized into 55 departments: one each for the 50 states, along with the District of Columbia, Puerto Rico, France, Mexico and the Philippines.

Over the years, the Legion has influenced considerable social change in America, won hundreds of benefits for veterans and produced many important programs for children and youth. Following is a chronology of significant dates in Legion history: