Thanks Roger, I had done a very rushed check and didn't find any place named Monticello in Sardinia either, but there is one in Corsica, which is french territory. That's good news, because if there was a place with that name and I were to use it in my novel, someone would call out my bluff with something wrong about it. What I intend to do is use Monticello for my imaginary village but say as little about it as possible. The important thing is what happens there during an holiday.
For another village in Portugal, the birthplace of Mariza, I'm using two real locations melded into one, and with a different name. I also use very common local old names for people, that nobody can really trace to any family. I think Thomas Hardy did something similar in his novels set in Dorset (but clever people have traced all his locations).
In the unlikely event of my novel becoming popular, I wouldn't like people going there to check the farms & families. It would be hideous...
In settings in London & Lisbon, I use real names of streets and squares and real descriptions. Anyone is welcome to go check where Mariza walked around... where she sat down, etc.