There is no school tomorrow in observance of Evacuation Day.
What is Evacuation Day?
March 17 is Evacuation Day, a holiday observed in Suffolk County (which includes the city of Boston) and also by the public schools in Cambridge and Somerville, Massachusetts. The holiday commemorates the evacuation of British forces from the city of Boston following the Siege of Boston, early in the American Revolutionary War.
Schools and government offices (including some Massachusetts state government offices located in Suffolk County) are closed. If March 17 falls on a weekend, schools and government offices are closed on the following Monday in observance. It is the same day as Saint Patrick’s Day, a coincidence that played a role in the establishment of the holiday.
The 11-month siege of Boston ended when the Continental Army, under the command of George Washington, fortified Dorchester Heights in early March 1776 with cannons captured at Ticonderoga. British 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.
The British evacuation 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 began was the first to be liberated.
Establishment of the Holiday
While Saint Patrick’s Day parades have been held in Boston since 1876, Evacuation Day was not declared a holiday in the city until 1901, amid interest in local history that also resulted in the construction of the Dorchester Heights Monument. The state made it a holiday in Suffolk County in 1938. The large Irish population of Boston at that time played a role in the establishment of the holiday. A 1941 law establishing the holiday in Suffolk County was signed in both black and green ink!
*For citations, please see this Wikipedia page.