For those of us who read every word of Laura Ingalls Wilder and her "Little House" series not once, but over and over (and then over and over again), we can be thankful that Wilder was not only a prolific letter writer, but that so many of the recipients of her notes saved them. Indeed, more than 400 letters still exist in private and public collections, many of which are excerpted in "The Selected Letters of Laura Ingalls Wilder," edited by Wilder biographer William Anderson.

His book appears at an opportune time for fans of the "Little House" books, with the 2014 publication of Wilder's autobiography, "Pioneer Girl," written in 1930, and the recent news that Paramount Pictures has plans for a movie based on her children's books.

In what is expected to be a final collection of unpublished writings from Wilder, the correspondence is organized by year, which is a logical presentation as her story unfolds. But it makes for slow reading during the earliest commentary, which predates the children's series and tends toward more perfunctory observations, some written on postcards during trips.

Still, some of the day-to-day comments are endearing, as this to her husband, Almanzo, when she is away: "Your warm underclothes are on your sock box in the closet. I don't know whether I told you or not. Please do remember to be careful about the fires." And later in same trip, "Don't worry about cleaning up the house. Let it go until I get back, only take good care of yourself and the dogs."

If you as reader can hang in there for the first 80-plus pages, you'll be rewarded with a behind-the-curtains look at how a book series is created. Wilder was the J.K. Rowling of the 1930s, with schoolchildren clamoring for the next volume, sending so many letters that her husband put in the largest possible mailbox at their home.

The collection begins with a letter from 1894, as Wilder, then 27, heads to Missouri with her young family. It ends in 1956, when she is 89, a year before her death. Except for the travel letters, most are written from her home, Rocky Ridge Farm in Mansfield, Mo. As readers, we see only her side of the correspondence, although the editor offers occasional insight.

"The Selected Letters of Laura Ingalls Wilder," edited by William Anderson

The charm — and importance — of letters as historical resource is that we see the writer at the most unguarded moments, commenting on daily life and the issues of the day, which is invaluable for insight into anyone, but particularly for an understanding of an author whom we tend to see frozen in time as the young Laura Ingalls.

She was, of course, much more, including a farmer, wife, mother and journalist.

But to her readers, she was a storyteller. The joy of this collection is the exchange of letters between Wilder and daughter Rose Wilder Lane, a successful author and journalist herself, who serves as her mother's writing mentor and first editor. Together they piece together the Little House stories, book by book, analyze the placement of characters, research the historical facts, debate the names of the books and discuss the marketing of the series. (Lane wisely suggests that Wilder have a photo taken for publicity.)

The letters reflect their intense collaboration while making clear that Wilder was in charge.

"I am afraid I am going to insist that the story starts as I started it," she writes. "How about rhythm and balance in the sentences? I was in hopes that I had profited enough by your teachings that my copy could go to the publishers, with perhaps a little pointing up of the highlights."

We are reminded of the tenuous nature of manuscripts in the days before copy machines and e-mail, as Wilder sends her daughter the only copy of "The Long Winter," and tells her to be careful. "All I have besides are my notes. Because my hand was so lame, I did not make another copy."

This collection of correspondence, with its discussion of altering events and characters to better tell the stories, addresses the nagging question of how factual the Little House stories are. The series, after all, is labeled fiction, although readers often look at the books as historical truth, a presumption Wilder encouraged. But when pressed by the publisher of the DeSmet newspaper in South Dakota, she admits, "The book is not a history, but a true story founded on historical fact."

Her wide-ranging correspondence includes responses to the author of the Look and See reading primers (Dick, Jane, Sally and the dog Spot), and to Dr. Irvin Kerlan, whose children's book collection was later donated to the University of Minnesota. There are letters to Twin Cities area folks, to a family in Pepin, Wis., and to schoolchildren around the world.

To her editor and agent, she corrects spelling errors in published volumes, tracks royalty payments and changes phrasing that, at a later date, she recognized had racist overtones.

Her books live on, although readers are no longer one generation from the prairie schooner themselves. The tale of a feisty, opinionated, adventurous girl, at its essence, is one of overcoming adversity, a story that shines through in her letters as well as her books.

"The way we live and your schools are much different now, so many changes have made living and learning easier," she wrote schoolchildren. "But the real things haven't changed. It is still best to be honest and truthful; to make the most of what we have; to be happy with simple pleasures and to be cheerful and have courage when things go wrong."

Lee Svitak Dean is editor of the Star Tribune's Taste section. Follow her on Twitter: @StribTaste.