There's a map I can't find right now showing the county-by-county distribution of Mormons in the US. It looks like a paint bomb was dropped on Provo and splattered across several adjoining states -- the MoZone. Then it quickly turns into sort of a fine mist over the rest of the country, with most places having from three to less than one percent Mormons.

Now look at this map showing dots for every person accounted for in the 2010 census. (Ignore the racial data.) Each dot represents a person.

http://www.slate.com/articles/news_and_politics/map_of_the_week/2013/08/segregation_in_america_every_neighborhood_in_the_u_s_mapped_along_racial.html

Notice how sparsely populated the MoZone is. Mormons are the kings of Utah, with large minorities in Idaho, Arizona, Nevada, etc. But it's such a small slice of American population.

I estimate 2 to 3 million members in the United States that claim to be members regardless of activity, sinning, or faithfulness.

This is an informed eyeballing of the numbers with the core as you state being in Utah. There aren't that many Utahns, about 2.8 million and at most 60% are self-identified Mormons, that's 1.7 million at the max in Utah. California, Idaho, Arizona, Washington, Texas and Oregon are the only other states with the possibility of more than 100,000 Mormons. Getting to three million US members is generous.