The MacMillan's brick fireplace was originally just a painted plaster fireplace in the first two or three years of the show, which would mean it wasn't brick when originally constructed.
Early on in the party scene, Mac and Sally indicate that they have lived in the house for about 10 years. That is contradicted by both the previous owner saying he did renovations 5 years earlier and the fact that the McMillans lived in a townhouse in the early episodes.
Actress Julie Newmar's name is misspelled in the opening credits as "Julie Neumar".
During the earthquake when the window breaks you can see a man duck into the bushes after he breaks the glass.
While they are playing Gin, Mildred is so busy talking that she deals too many cards to Enright at the beginning of the game.