Last Skeleton Key Door Locks

I presume you mean "bit key locks".

(I don't have an answer, but you're more likely to find the answer if you're searching for the right terminology...)

Also, are you asking about door locks or exterior door locks? These continued to be used as privacy locks after they were being phased out as security locks, I believe.

(My apt. has them on closet doors only.)

Yes, I guess I meant "bit key locks". I was asking about BOTH exterior doors AND as interior privacy sets. When were they last used in new homes in the USA? Were rim sets and mortise locks phased out at the same time?

I'm not interested in their use in Europe; they were never phased out as warded exterior/security bit key locks were simply replaced with modern multi-lever tumbler locks, which are still bit key operated.

C.W.

You don't see "bit key" locks used much at all in houses built after the 50's.

But what about bit key locks used as interior privacy sets?

Same deal. Unless you want to include the modern privacy sets that open with any tool that fits in the slot to be "bit key" operated.