(Gray counties had insufficient data to calculate Partisan Voting Indexes (PVIs)).
For most of the first half of its history as a state, Utah had swingy PVIs. Kane County, the county in the center on the southern border, was until recent decades the most Republican county. Utah began its Republican trend in the 1950s and continued trending Republican for most of that time since. 2016 backslid a little, but I did not include the votes for Evan McMullin (I), who took 22% of the vote here.
Salt Lake County has diversified in recent decades and is now politically diverse. The northern parts of the county, including Salt Lake City proper, South Salt Lake, and West Valley City are very Democratic, as is the ski town of Alta further south. Many cities in the south of the county are more suburban, white, Mormon, and conservative. Herriman and Bluffdale are isolated from the rest of the county and are dark red.
Summit (Park City) and Grand (Moab, Arches, Canyonlands) have been light red or light blue in recent elections because of the environmentally conscious and tourist town voters.
San Juan County in the southeast is one of the lesser Republican counties because of a significant Native population and the lowest per capita income of any county in the state.
The one medium-dark blue county in the mid-20th century maps is Carbon County, where many immigrants from Italy, Greece, and the Balkans as well as their descendants worked in the mines. Tooele County, to the west of Salt Lake County, also has some mining history.
PS: I don’t know why 1992 appeared a second time, where 2000 should be.
Here are the results in table form.
Here are the results in slide form.