The newest U. S. census is 1940 which became available in April 2012, 72 years after the census was taken. In that census Thorstein, Ruth and their 2 children lived with Andrew and Hilda in Chicago. The children were Warren age 5 and Marilyn age 2.
A Warren Guy OLSEN married Mary Ann WALTON on 20 Aug 1955 in Cook County, Illinois. Chicago is in Cook County.
Two women named Marilyn Olsen married in Cook County. One was Marilyn J. to Robert V. BURNS on 25 Feb 1955 and the other was Marilyn R. to Robert J. KELLIHER on 4 Sep 1956.
To simplify searching for descendants and not waiting another 23+ years for the 1960 census, you could try to locate Thorstein's obituary. According to our Social Security Death Index (SSDI) a Thorstein Olsen, born 8 Dec 1908, died 1 Feb 1990, possibly in LaGrange, Illinois.
You could email the LaGrange library and ask, if they have a copy of Thorstein's obituary, could they scan you a copy. Check http://www.lagrangelibrary.org/lagrange/askus.asphttp://www.lagrangelibrary.org/lagrange/askus.asp for more information.