A Twitter post from @Archispeak asking “Who coined the term “stately home” and when?” prompts the Times to delves into it’s archives to try and find an answer.
The earliest mention in their archives is from February 1847 in a story relating the terrible destruction by fire of Easton Lodge in Essex. A gallery of images of the house can also be found on the ‘Lost Heritage’ website: Easton Lodge
As to whether 1847 is really the earliest use of the term it seems unlikely – I’m sure with a bit of research something earlier can be found.
Blog post: ”Who invented the “stately home”?’‘ [The Times]