Trumbull, Connecticut, Bridgeport area. The house that inspired the book by Eric Hodgins is located at 240 Indian Trail Road in New Milford, Connecticut. Original building budget $11,000, final cost $56,000. In 1939 dollars. Hodgins was forced to sell the house in 1945 for $38,000. He tried to buy it back with money from the sale of the book to RKO but the owner wasn't interested in selling.
Rocky Mount, North Carolina. Check out this link for details-https://www.digitalnc.org/blog/mr-blandings-dream-house-rocky-mount-nc/ also-https://mainstreetrockymount.com/2017/08/15/mr-blandings-builds-his-dream-house-in-historic-west-haven-part-1/ and https://mainstreetrockymount.com/2017/08/16/mr-blandings-builds-his-dream-house-in-historic-west-haven-part-2/
Spokane, Washington. Details here-http://www.historylink.org/File/9031 and http://spokanehistorical.org/items/show/500. Magazine ads in 1948 noted that another Dream House was set to be built in Seattle by First Mortgage Co. and furnished by Bon Marché but newspaper archives for Seattle don't have any mention of any such house being built or advertised.