Watch out Salt Lake County, Utah County is gaining on you â and in the next 50 years will become almost as populous. By 2065, Salt Lake County is projected to have 1.69 million people (from just under 1.1 million in 2015), with Utah County only slightly behind at 1.62 million (up from 586,000 now). Thatâs according to population projections released Monday by the Kem C.