I was a Deputy Sheriff in another State for 7 years. In most states, the state constitution names the sheriff as the Chief Law Enforcement Officer in their County and gives him his authority and responsibility. Here is a quote from a Michigan Sheriff's website.
The Sheriff has Jurisdiction across his entire county and is said to be the Chief Law Enforcement Official of the county and having the ability to be the “Buffer” between the People and Government. While Upholding the rule of law for the government, the Sheriff also has the ability to uphold the Constitutional rights of the People to protect them from Government Over-reach on a Local, State and Federal Level.
In the PRNJ, the Chief LEO is the prosecutor. According to the state of NJ: Under New Jersey law, the county prosecutor functions as the chief law enforcement officer for the county. Each county prosecutor is charged with the obligation to use all reasonable and lawful diligence in the detection, arrest, indictment and conviction of people who violate the criminal laws of New Jersey.
Also in PRNJ, the prosecutor is appointed by the Governor.