From My Country 'Tis of Tee: Patriotic Melodies (Library of Congress), with bibliography, and links to sheet music, song sheets and sound recordings:

Although we know that Reverend Samuel Francis Smith wrote the words to "America" (also known as "My Country 'Tis of Thee"), the origin of the song's melody remains a mystery. And the history of its verses is even more complex.

The son of Henry Carey, a British singer-composer, claimed his father was the first to compose both the words and the music and introduced them in London in 1740 as "God Save Great George the King." However, Carey's son had financial reasons for making such a claim, and music historians argued it was more likely any such tune would have been based on a pre-existing melody.

Such an earlier melody, if it did exist, has been attributed to various seventeenth-century sources including the English composer John Bull, the French court composer Jean-Baptiste Lully, and even a military hymn from Switzerland. Although the tune's exact origin is not confirmed, it was printed in England in 1744 in the tune book Thesaurus Musicus.

The performance that led to the explosion in popularity of "God Save the King" took place in London in September 1745. Dr. Thomas Arne arranged the tune for a September 28, 1745 performance at the Drury Lane Theater and it was also performed at the Covent Garden Theater for several nights running. The song was intended to show support for the Hanoverian King George II, following the defeat of his General John Cope at Prestonpans, a battle that was the opening salvo in the war against "Bonnie Prince Charlie," his Stuart rival for the throne.

Before the music of "America" made its way to the United States it was played in many countries. By the 1790s the melody had become that of the Danish national anthem "A Song to be Sung by the Danish Subjects at the Fete of their King, to the Melody of the English Hymn." Eventually it also became the national anthem of at least six other places, including Prussia ("Heil dir am Siegerkranz" or "Hail Thee in Victor's Wreath"), Britain ("God Save the Queen") and Liechtenstein.

The first documented version of this melody printed in the American British colonies dates from 1761. The tune of "God Save the King" was used, in a slightly modified form, as the melody for the hymn known as "Whitefield's tune," published in Urania, a collection of sacred songs compiled by James Lyon and printed by William Bradford.

~Masato