Robert Heinlein, a prolific science fiction author in the 40's through 60's, had a soft spot for Mormons, and wove them into many of his stories. It's one thing that endeared me to his writings, to have someone who actually thought Mormons would still exist in the future.
For example, in "Menace from earth", a celebrity is being shown around the moon colony, and is given directions to her hotel: go past the embassy and turn left at the Mormon temple...
In a book I just read last week, Sixth Column (first published in 1941), the US has been taken over by "Pan Asians", and a small group of Americans is using a fake religion to recruit people to join in an insurgency. One of the characters is told to go to Salt Lake City for a recruiting trip.
"Just a minute. Why Salt Lake City?"
"Because I think it's a good spot for recruiting. Those Mormons are shrewd, practical people and I don't think you'll find a traitor among them. If you work at it, I think you can convince their Elders that the great god Mota is a good thing to have around and no menace to their own faith. We haven't made half enough use of the legitimate churches; they could be the back bone of the movement. Take the Mormons--they run to lay missionaries; if you work it right you can recruit a number of them with such experience, courageous, used to organizing in hostile territory, good talkers, smart. Get it?"