Sort of. There are very few scenarios where I can imagine one nuclear bomb being dropped on a US target, accident by our own military seems most likely followed by terrorism then a suicidal nuclear power, and in all three of those scenarios I doubt the bomb would hit where any planning suggests it would.
A nuclear bomb (several hundred times larger than the one dropped on Hiroshima) was accidentally dropped in the US in 1961[1]. Luckily it (obviously) didn't detonate.