Bellone had 57 percent of the vote to Carpenter's 43 percent.
Both were vying to replace Steve Levy, who has been occupying the county executive office since 2003.
A Democrat turned Republican, Levy lost his bid for governor before announcing he'd step down at the end of his term.
Bellone, currently the Babylon town supervisor, outspent Carpenter, the current county treasurer.
Now, he faces a budget with an estimated $135 million gap between revenues and spending.