The book and movie,"The Bridges Of Madison County" by Robert Waller made these covered bridges famous, but they have long been an attraction. Located in Madison County near Winterset, Iowa just southwest of Des Moines, they have attracted tourists for many years. Originally there were 19 of the covered bridges but only 6 remain. You can seen pictures and read more about them on this site.
Everything you want to know is on this site. There is an annual covered bridge festival and this year it will be Oct. 14-15. While in the area you might also want to visit John Wayne's birthplace.
This area is well known for their quiltmakers as well.
If you are looking for a great fall trip, go to see the covered bridges in Madison county and while you are there search out the other interesting attractions of this area.