With syncope (probably through influence from the Swedish name Köklax) from *Kaukalaksi, from *kauka(“long”) (in modern Finnish kauko-(“far, distant”)) + *laksi(“bay”) (older form of lahti).[1]
The internal locative cases (inessive, illative and elative) are used with this place name when referring to a location; for example, "in Kauklahti" is Kauklahdessa.
^ Sirkka Paikkala, editor (2007), Suomalainen paikannimikirja [Book of Finnish Place names] (in Finnish), Helsinki: Karttakeskus, Kotimaisten kielten tutkimuskeskus, →ISBN