chief (of a police station, fire station, etc.); head (of an office)
Refers to the head of a specific government office or station, most commonly a police chief. The exact office is usually clear from context.
The new police chief has taken up his post.
The fire chief took command at the scene.
He is the chief of the Shinjuku Police Station.
She served as chief for three years.
He took office as the new chief.
署長 and 所長 are pronounced identically (しょちょう) but 所長 is the general head of any office or institute, while 署長 specifically means the chief of a station like a police or fire station.
Compound of 署 (government office, station) and 長 (chief, head).