As a kid, I was always a big fan of the Little House books. Now, as an adult, I’d like to find a similar thing, but written toward a more adult audience.
So, I’m looking for readable, autobiographical “frontier life” stories - not historical fiction, and not necessarily stale diaries or letters. Is there something “based on real life” but prose-ified out there that fits this bill?
“Mandingo Goes West”
I liked The Diary of Mattie Spenser (fiction) and These is My Words (fictionalized account of a real person).
Ooh! I highly recommend Plains Woman: The Diaries of Martha Farnsworth, edited by Marlene and Haskell Springer. I just read this recently, and enjoyed it very much.
Martha kept diaries from her days as a young teenager to a year before her death (in her late fifties/sixties, I think), and this book offers excerpts from them with only a few editorial comments. It’s a fascinating and very readable book, as Martha is a funny, smart writer who is very honest about everything from the many boys/men she willfully led on, to the hardships she suffers from her alocholic first husband, to the death of a loved one (the anniversary of which she heartbreakingly remembers every year) and the happy times she finally has with her second husband.
(A good site where I learned more about Martha Farnsworth is the Kansas Historical Society, which is where the original diaries can be found on microfiche.)
And btw, there’s nothing wrong with re-reading the Little House books. I do it every couple of years! 
Or, you might try one of the biographies of Laura Ingalls Wilder, one of the most acclaimed being Becoming Laura Ingalls Wilder by John Miller.
Let us know what you find! I’d love to hear of any other discoveries in this genre.
I actually just re-read the “little house” books a few months ago (for a 24 year old man, it’s an odd sight), and that actually got me interested in reading some stuff that wasn’t so conspicuously aimed at and framed for kids (Laura marries Almanzo, and skip to a year later, there’s magically a baby!). I’d like a more adult, realistic slice. I’ll check out those rec’s!
Although it’s fiction, you should check out Jump-Off Creek by Molly Gloss. It’s about a female homesteader in Oregon. It’s a well-researched, beautifully-written book. I believe Gloss based it partly on her own ancestors’ experience.
The diaries of Elizabeth “Libby” Bacon Custer, the widow (for many many years) of George Armstrong Custer, are in print and have many tales of life on the frontier, encounters with Indians (politically incorrect by today’s standards, of course) and the Civil War. Also, The Gentle Tamers by Dee Brown (most famous for the book Bury My Heart at Wounded Knee is an excellent book on real women of the west from frontier wives to mail order brides to prostitutes to Mormon polygamists to outlaws.
I know you said you didn’t want fiction, but I’ll name this anyway because it is so well researched and absorbing that it’s one of the greatest frontier narratives in American literature: Conrad Richter’s The Awakening Land trilogy. This isn’t a work that you’d find Fabio modelling for the cover of- it’s the story of Sayward “Saird” Luckett, the daughter of a half-breed Pennsylvania farmer with a chronic itching foot, and her life on the frontiers of the Ohio from the time she and her sisters are the only white women in an overgrown forest til the time she is an old woman and the same frontier is a congested city. She marries Portius Wheeler, a freethinking “Bay State lawyer” with a past, has many children, and by the end of the series you feel you’ve lost a friend. Fantastic books that also inspired one of the best and most realistic miniseries ever made (it starred Elizabeth Montgomery & Hal Holbrook and its sets, houses, dialects, mindsets and costume are incredibly accurate, putting it leagues above such schlock as *
North & South*).
Link provided because there’s more than one book called The Emigrants – a bit bleak and heartbreaking, but I think prairie life was like that, especially at first.
My Antonia by Willa Cather is a good one.
I’m always pushing The Homesman on people. It’s by Glendon Swarthout. A homesman is someone who escorted wives and mothers back east after they were broken by prairie life.
Robert Morgan’s books are good but they’re set in Appalachia rather than prairie lands, and I guess Appalachian books are a whole other subject. They have some of the same feeling though, just not so much sky.
Oops, just re-read the OP and realized you were looking for non-fiction. [tiptoeing quietly away]