Bosaint is wearing a uniform with patches that say "Police" and collar pins that identify him as the Sheriff; he also drives a car which says Sheriff. The inconsistencies in the uniforms are the same with the deputies. In the United States, Sheriffs do wear uniforms that say "Police". Also the Sheriff would not be called "Chief".
At about 23:45, after Scully has finished taking her bath, she walks past a mirror and a crew person wearing a blue shirt is briefly visible.
At approximately 9:30, when Scully first talks to the sheriff after reviewing the security footage, she refers to him as "Captain Bonsaint", but his name badge shows his position is "Chief" and this is how he is later addressed at several other times, including by Scully.