KJV translators took mansion from the Latin Vulgate.Thanks. It makes sense that the definition of "mansion" has changed over a couple thousand years. The sentence "In my Father's house are many mansions" just seemed odd to me.Strong's 3438 - μονή - translates to abode. Literal translations of the Bible render the Greek as rooms or dwelling places.
Mansions seems exclusive to KJV, and in part derives from the Middle English word Manse (from the Latin mansus, denoting house or dwelling). Mansion is just a rectory or vicarage, not actually a large estate.
To my mind, μονή denotes dwelling with the Father for all the saints, who are priests in the kingdom.
14:2 In domo Patris mei mansiones multæ sunt; si quominus dixissem vobis: quia vado parare vobis locum.