The local exteriors were shot at Big Sky Ranch in California. The Ingalls homestead and Walnut Grove town facades were built in April and May of 1974. These buildings were not filmable inside as they were wooden shells. So, interiors were shot at Paramount Studio, in Hollywood, on Stages 31 and 32. Using aerial photos of the set, found at http://www.pioneerontheprairie.com/above_below.htm, and my general knowledge of the show, I have created a map of the Walnut Grove set which once stood at Big Sky Movie Ranch, Simi Valley, CA.
A Walnut Grove Set Map (Poster) can be downloaded here.
A Walnut Grove Set Map (Poster) can be downloaded here.