McKinnon ni a bi ati gbe ni Long Island ilu ti Okun Cliff, New York si Laura Campbell, a obi olukọni, ati Michael Thomas Berthold, ohun architect. O ni o ni a younger arabinrin, Emily Lynne. Baba rẹ ku nigbati o wà 18 years old.As a child, McKinnon dun orisirisi ohun elo. O bẹrẹ si mu awọn piano nigbati o wà 5 years old, awọn cello nigbati o wà 12, ati ki o kọ ara rẹ bi o lati mu awọn gita nigbati o wà 15. O si kẹkọọ lati North Shore High School ni 2002, ati lati Columbia University ni 2006 pẹlu kan oyè ni awọn ere idaraya, ibi ti o co-founded a comedy ẹgbẹ, Tea Party, eyi ti o fojusi lori improvisational awada. Ni Columbia, o starred ni mẹta Varsity fihan: V109 "Dial fun Deadline D110", V110 "Off-Broadway" ati V111 "The Sound of Pranges".
Ìpàdé Tea Party