NBC (ended 1983)
The distance finding website indo.com says that Mankato and Walnut Grove are 74 miles apart, as the crow flies. Mapquest driving directions say 82 miles.
My husband is a geography teacher and often references an aerial photo website called globexplorer.com. You can go there, put in a town name, and get a current aerial view. It's more up-to-date than most sites like it. Just for fun, my kids and I have checked out Walnut Grove (pretty tiny at pop. 625!) , Sleepy Eye, and other LHOTP related towns. Hometownlocator.com is another great site; the aerial photos are older, but there's lots of info on every town you can think of, largely using US Census stats, county records, and chamber of commerce info.
A saddle horse is only good for about 20 miles per day, and that's a workout, plus he has to eat and rest, you can imagine the toll on a team pulling a loaded down buckboard.
Charles even made some night trips which is hard to believe.
While on a vacation to MN in the late 80's, I took a trip to Walnut Grove and it is a very small town and it did have a small museum, which actually i was disappointed in. It didnt really have hardly anything from the Ingals family, only things that came from that era. WG is located in the south west corner of MN. Having to travel east to come back home, we went through all the other towns mentioned on the show..Sleepy Eye, Mankato.
Somewhere in Wis. , I believe, there is a town that also promotes Laura Ingals , where she had lived in her later years. I forget what the name of it is, but they also had a house that had small museum/info. I bought a small book there about her and all the places she had lived , but would have to do some major digging to find it.