But the state's colleges and universities also have the highest number of students still enrolled at the six-year mark.
READ MORE: Utah Regents push higher credit loads to boost graduation rates
The report shows what many Utah residents already know, said state higher education officials: that a good chunk of students hold down jobs during their college years. Many of those students and others interrupt their studies to serve two-year Mormon missions.
"Most of our students are working," said David Buhler, commissioner of the Utah System of Higher Education. "That can slow them down a bit."
After missions, others "come home at 20 or 21, they get married, and then they finish college."
READ MORE: As state money is slashed, Utah students are paying more of college cost
About 60 percent of full-time Utah students get their undergraduate degree from four-year institutions within six years, according to the study released Thursday from the National Student Clearinghouse Research Center. It tracks students who like Casper, began college in fall 2007.
That's nearly 20 percent behind the national average and on the heels of Montana. New Mexico and Oklahoma also lag behind, both hovering just over 70 percent. On the other end, Iowa leads the pack with about 91 percent.
The state fares slightly better in the national context when part-time students are considered.
In Salt Lake City, state officials don't know exactly how many students break from studies to serve Mormon missions, Buhler said, "but we know it's a significant number, enough to skew these" numbers.
READ MORE: Tuition waivers help USU offset Mormon missionary losses
Other students sign up for fewer classes per semester or take time away from school to work, prolonging graduation. Most students hold at least a part-time job.
The Church of Jesus Christ of Latter-day Saints last year lowered the minimum age for missionaries from 21 to 19 for women and 19 to 18 for men. Buhler expects more missionaries to serve right after high school, possibly improving the rate.
And officials are working to speed up the process. Most four-year Utah institutions now charge students by the semester, instead of by individual credit hours, encouraging them to take more classes at once.
Raising the six-year graduation rate is "our most central goal," said Ruth Watkins, senior vice president for academic affairs at the University of Utah. Many students there have already started families. Half marry before they graduate, she said, and one in four students have a child. The university is gearing a new set of scholarships at students who are just a few dozen credit hours away from a diploma.
READ MORE: Utah women graduate from college less often than male counterparts
The school's graduation rate within six years mirrors the current state level. But within an eight-year period, Watkins said, that rises to about 70 percent, indicating that students do end up graduating.
"Our students are remarkably focused, hardworking people," she said, "and they are not giving up on education."
Another Utah factor: remedial work
More past stories from The Salt Lake Tribune:
Too many Utah college students aren't ready for rigor
U. of Utah graduation rate sags in face of poor college readiness