What counties elect sheriffs in the US?

In the United States, a Sheriff is a county official and is typically the top law enforcement officer of a county. Historically, the sheriff was also commander of the militia in that county. Distinctive to law enforcement in the United States, sheriffs are usually elected. The political election of a person to serve as a police leader is an almost uniquely American tradition.

Additional: I believe that all US Sheriff's are elected and in many (all?) states the office is provided for under the Constitution of the State. The office of Sheriff is distinctly different from that of a Chief of Police, which is strictly an appointive position.