Wikipedia has this to say about Sheriffs (of United States, not Nottingham :)
In the United States of America, the scope of a sheriff varies across states and counties. The sheriff is always a county official, and serves as the arm of the county court. The sheriff always performs court duties such as administering the county jail, providing courtroom security and prisoner transport, serving warrants, and serving process. In urban areas a sheriff may be restricted to those duties. Many other sheriffs and their deputies may serve as the principal police force.
As such, is there any difference between a Sheriff and any other officer in charge of county police (the above quote seems to imply the reporting difference, e.g. one would report to the court and one to the county administration)?
Or is the difference merely in whether the post was called "Sheriff" historically in a given locale but with no functional distinction?