BYU's total enrollment is about 33,000. LDS% has to be in the high 90s, so say 28,000 LDS students.
Utah's total enrollment is about the same. There's no way the LDS% is as high.
UVU's total enrollment is 40k. They probably have a higher LDS% than Utah, so again, they're probably ahead.
But outside of Utah county, the University of Utah probably has the most LDS students (BYU-Idaho has 20,000 students, so it might be close, but USU has 28,000 and I suspect their LDS ratio is similar to Utah's, maybe slightly higher).