The holiday was originally celebrated on April 19, the actual anniversary of the battles (fought in 1775). Since 1969, it has been observed on the third Monday in April in Massachusetts and in Maine (which until the Missouri Compromise of 1820 was part of Massachusetts). The Monday holiday creates a three-day long weekend. It is also the first day of a vacation week for public schools in both states and a school holiday for many local colleges and universities, both public and private.
Observances and re-enactments of the battles occur annually at Lexington Green in Lexington, Massachusetts (around 6:00 am) and the Old North Bridge in Concord, Massachusetts (around 9:00 am). In the morning, mounted re-enactors with state police escorts retrace the Midnight Rides of Paul Revere and William Dawes, calling out warnings the whole way.
The most significant celebration of Patriots' Day is the Boston Marathon, which has been run every Patriots' Day since April 19, 1897 to mark the then-recently established holiday, with the race linking the Athenian and American struggles for liberty (marathons being so named after the Greek Battle of Marathon).
In 1894 the Lexington Historical Society petitioned the Massachusetts State Legislature to proclaim April 19 as "Lexington Day." Concord countered with “Concord Day.” Governor Frederic T. Greenhalge opted for a compromise: Patriots' Day. Patriots' Day was first proclaimed in Massachusetts in 1894 by Gov. Greenhalge replacing Fast Day as a public holiday. The idea was introduced to the Governor by the statesman from Lowell, Isaac Henry Paige. It was established on April 19, commemorating the date of the Battles of Lexington and Concord in 1775, and consolidating the longstanding municipal observances of Lexington Day and Concord Day. It also marked the first bloodshed of the American Civil War in the Baltimore riot of 1861, during which four members of the Massachusetts militia were slain and 36 injured. The dual commemoration, Greenhalge explained, celebrated "the anniversary of the birth of liberty and union." In 1938, with the generation that had fought in the Civil War largely off the voter rolls, the Massachusetts legislature passed a bill establishing the holiday "in commemoration of the opening events of the War of the Revolution."