I think HeyyyUguyyys is mostly right. I’ve lived in Seattle, the Bronx, outside of Philadelphia, and Memphis, and while there was typically a fellow Utah fan or two I could find, it was always a small group.
I think the only 2 things that would drive up numbers in a given area outside of Utah are: 1) areas where outdoor recreation are popular (as that’s a primary reason someone that grew up out of state is drawn to the U, and they will likely choose to live in areas with similar opportunities after), and 2) areas that have an above average LDS population (as a sizable portion of Utah alumni are LDS).
As time goes on, I think the influence of #2 will slowly decrease while the influence of #1 will slowly increase. But for the most part, I think the fanbase isn’t all that big outside of Utah.