Carl Bridenbaugh's The Spirit of '76 gives some earlier instances of the
use of America and American. Early 17th-century Puritan authors used
both terms a lot, but they meant "New England" when they did--not all
the colonies. A good many associations and organizations formed between
1760 and the Revolution used American in their names and publications:
e.g., "The American Company of Comedians" (1763); "American
Philosophical Society" (1768); and "American Medical Society (1771).
Doug Deal