March 17 is Evacuation Day in Massachusetts, United States.
This day commemorates the evacuation of the British troops from the city of Boston on March 17, 1776, at 3:17 P.M.
“The 11-month siege of Boston ended when the Continental Army, under George Washington, fortified Dorchester Heights in early March 1776 with cannons captured at Ticonderoga. General William Howe, whose garrison and navy were threatened by these positions, was forced to decide between attack and retreat. To prevent what could have been a repeat of the battle of Bunker Hill, Howe decided to retreat, withdrawing from Boston to Nova Scotia on March 17.
“Boston was one of the most important ports in the New World, and one of the most defensible (there is only a single channel into Boston Harbor which is ringed with islands). That the Americans were able to drive off several thousand hardened troops and 1,100 loyalists with only a few warning shots fired and no loss of life or property was a major accomplishment and was Washington’s first victory of the war. It was also a huge morale boost for the Thirteen Colonies, as the city where the rebellion against England started was the first to be liberated. Boston was never attacked again.” 
Evacuation Day is an observed holiday in Suffolk County. Schools and government offices are closed.