Thanks to Jonathan Daniel of Pittsburgh PA for the following information about Louis Stevens.

The Architect of River Ridge Mansion

Louis Stevens

The following is from the “Pittsburgh History & Landmarks Foundation PHLF News”
newsletter No. 162, March 2002, pp.16 & 18.

Louis Stevens (1880–1961) was born November 4, 1880 in West Brownsville, Washington County, PA.
Stevens established his architectural practice in Pittsburgh in 1906; he retired in 1952.
He died August 28, 1961; he was living at Lynn Run Road, Rector, PA.

To view a map (created by Jonathan Daniel) of other properties designed by Louis Stevens, please select this link:

The following is from “Pittsburgh of Today, Its Resources and People”, Vol. 3, by Frank C. Harper, Copyright 1931.