Bucks is the standard contraction for the English county of
Buckinghamshire.
William Penn, founder of the state, had his roots in the Buckinghamshire village named for his family, near
High Wycombe. Thus, stretching American naming norms a bit, there exist both Bucks, Penn. and Penn, Bucks. Which latter, as it happens, is not so far away from
the place I used to call home before I moved
somewhere with better beer.