Commissioner is commonly used.
Yes, the president is considered the chief law enforcement officer of the United States.
The Chief officer was Henry Wilde.
The chief law enforcement officer of California is the state attorney general, currently Kamala Harris.
The chief accounting officer of a business is also called the controller.
No. Police officer is not a proper noun
The County Sheriff
the sherif
the sherif
Attorney General
District Attorney
The chief administrative officer of a township is a Trustee.
In most counties the Sheriff or District Attorney is the chief law enforcement officer for the county. In most states the State Attorney General is the chief law enforcement officer for the state.