Although he is a fan of the show, Montalbano creator Andrea Camilleri has openly stated that Luca Zingaretti's characterization differs somewhat from how he had originally envisioned the character. Camilleri poked fun at this in one of the books, where it's acknowledged that the TV series exists in the Montalbano universe. Specifically, Montalbano himself states that, unlike Zingaretti (who's also 11 years younger), he has a full head of hair.
While the geography of Vigàta and Montelusa in the books is based on Porto Empedocle and Agrigento, the series is shot primarily in the city of Ragusa.
When the core cast was selected, Alberto Sironi, the director, brought them to the RAI TV offices for an introduction, and the first response was a bit cold because the actors were younger than the age described in the novels. Still, in the end, they agreed with his choice. Then when he found the locals he wanted to use in the series as extras or minor characters, he again brought them to the main offices, and the heads were worried the public from home could not understand their dialect. He said he wasn't worried about it trusting the stories' strengths.