I'm a millennial too (a grandmillenial, I think, ahaha - born in 85) and grew up in the Southern US. There were piles and piles of Katies everywhere. Some were just Katie, some were short for Katherine/Kathryn etc., and I'm sure some were short for the Caitlin names. Katherine is pretty standard down here, though.
I am a huge fan of Kate, but not so much of Katie.
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