I stumbled on the real reason the Mormons were thrown out of Illinois in a book "The History of Banking" as sort of an aside.
In that era the country had yet to completely settle into a monetary system.
Banks, cities, states, etc., all had their own currencies as did the Mormon group in Illinois.
There were exchange rates, and if a business or person was paid for a service or product with money from one entity, he could exchange that for that of another.
Except when dealing with the Mormons.
When a person tried to redeem currency they had been paid by a Mormon at a Mormon bank, they were sent away, being told that the money was for the convenience of their members and worthless for anyone else.
The mormons also printed the first Three dollar bill, which later gave rise to the statement...”As queer as a three dollar bill.”
Once in Utah the mormons began raiding wagon trains. The most infamous raid was the Fancher train in which all the adults and some of the kids were massacred. Known today as the Mountain Meadows Massacre. They also made raids on the Miltmore and Shepherd wagon trains which no one hears about.
During the Civil War the pro-South Mormons also armed the Navajos and sent them to raid Union forts in that area, causing the Union to send in Kit Carson with troops to round up the tribes and move to the Bosque at Ft Sumner NM. The tribes still whine about that even today.
Follow The Money.