I watched a few bits and pieces of TVLand's "Benson" marathon last weekend, and the governor's mansion (exterior) looks a lot like Alex Benedict's mansion in "Etude in Black." I don't know if my eyes were playing tricks on me, or if it could have been the same mansion.
Sherlock, the "Murder By The Book"/"Most Crucial Game" house is the one I was talking about before -- it was also in "Prescription: Murder". You'll find a whole discussion of that house in the Scrapbook article, "Columbo Flashback". It's called Stahl House.
The mansion used in "Etude In Black" is the same mansion seen in "Benson" and if I'm remembering correctly, it is also the house used in "Fresh Prince Of Bel Aire". That house pops up a lot in TV shows and movies. However, it is NOT the same house as Jarvis Goodland's in "Greenhouse Jungle". I myself made that mistake but then I looked at it closer. The Goodland house is not the same as the Bennidict house. They do look alike however.