Her father is Liberian. Her mother is from a Russian Jewish/Polish Jewish family, and Kat was raised in her faith. Her paternal grandfather was a UN Ambassador, serving for 40 years in The Netherlands, Sweden, Romania, and Kenya.
Tattooed on her inner left wrist is the inscription, "nosce te ipsum", which is Latin for "Know thyself.".
As of May 2022. Graham has announced her engagement to Director Darren Genet. They had been dating for nearly 5 years.
She has a half-brother, Yakov, born in Tel Aviv, Israel.