[RedMDer]

In most cases the chief of police is appointed “hired” by the local elected officials while the sheriff is elected by the people and funded by the state government.
So I would guess the local elected officials have much less influence over the sheriff.

[GOYAKLA]

It is entirely as you say! In my terminology it is Politicians selecting their Butt Boys, who walk the line, where as Sheriffs are elected by the people. Most Sheriffs know this and do the will of the people.
See link for example of a Sheriff that people re-elect
http://www.snopes.com/crime/cops/judd.asp