Where Did Francis Scott Key Write the "Star-Spangled Banner?"

Indian Queen Hotel, Baltimore

He jotted some thoughts down in Baltimore Harbor, but finished the song that would become the National Anthem at Baltimore’s Indian Queen Hotel.  Liz Williams explains at the blog of the National Museum of American History:

John Gadsby, most famous for entertaining the likes of George Washington and Thomas Jefferson at Alexandria’s City Hotel, arrived in Baltimore in the fall of 1808. He took over management of the Indian Queen Hotel, located at the corner of Hanover and Baltimore Streets (known better now as the site of the former Mechanic Theatre).
In 1827, The Baltimore Gazette recognized Gadsby as “the first man who introduced the proper style and taste for public entertainments in this city.” It was a large hotel, and over time Gadsby introduced new features to the business, including a mechanically powered coffee roaster, reading room, and public baths. The operation was large and Gadsby owned 42 slaves, most of whom worked at the hotel.
It was here, at this hotel, that Francis Scott Key found a bed for the night after arriving on land on September 16th. In his room, he compiled all of his notes and finished writing out his four verses. The lyrics were published the next day with no title, but it was soon given one by a friend: Defence of Fort McHenry. It was noted that the lyrics could be sung to the music of a well-known British club song called “Anacreon in Heaven.” And the rest, as they say, is history.