On June 14, 1777 the Second Continental Congress at Philadelphia representing the thirteen colonies then situated along the eastern seaboard with the exception of Maine (1820) and Florida (1845) passed the following resolution:
“Resolved, That the flag of the United States be thirteen stripes, alternate red and white; that the union be thirteen stars, white in a blue field, representing a new Constellation.”
Eighteen years later the U.S. Flag Act of January 13, 1794 was signed by President George Washington altering the flag design with the admission of Vermont (1791) and Kentucky (1792) into the Union providing for fifteen stripes as well as fifteen stars.
“An Act making an alteration in the Flag of the United States Be it enacted by the Senate and House of Representatives of the United States of America in Congress Assembled, That from and after the first day of May, Anno Domini, one thousand seven hundred and ninety-five, the flag of the United States, be fifteen stripes alternate red and white. That the Union be fifteen stars, white in a blue field.”
Thus on June 18, 1812 with a declaration of War with England there were only 15 stars and stripes represented on the Fort McHenry flag, though there were actually 18 states with the admission of Tennessee (1796), Ohio (1803) and Louisiana (1812).
On April 4, 1818, a new Flag Act was signed by President James Monroe provided what is still honored today:
An Act to establish the flag of the United States. Be it enacted by the Senate and House of Representatives of the United States of America, in Congress Assembled, That from and after the fourth day of July next, the flag of the United States be thirteen horizontal stripes, alternate red and white: that the union be twenty stars, white in a blue field. And be it further enacted, That on the admission of every new state into the Union, one star be added to the union of the flag; and that such addition shall take effect of the fourth day of July then next succeeding such admission
In 1907 the descendants of Lt. Colonel George Armistead, the commander of Fort McHenry during the war, presented the original star-spangled banner to the Smithsonian’s Museum of American History in Washington, D.C. A replica of this flag is flown by the National Park Service at Fort McHenry National Monument and Historic Shrine in Baltimore, Maryland. by Presidential Proclamation day and night.
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Maryland in the War of 1812 