The US will be 238 years old on September 3, 2011, which is the 238th anniversary of the Treaty of Paris (1783) which ended the Revolutionary War and granted (or won) US independence as a separate and independent nation. The signing of the Declaration of Independence is highly celebrated, the signing of the Treaty of Paris, not so much.
The traditional birthday of the Marine Corps is 11-10-75, November 10, 1775, when the Second Continental Congress created the Continental Marines. However, after the Revolutionary War, in 1783, both the Continental Marines and the Continental Navy were disbanded and ceased to exist. Congress created the United States Marine Corps 15 years later in 1798. So to state that the "Marine Corp," the United States Marine Corps, is older than the United States is, at the very least, a misnomer.