The second series of "Jonathan Creek" was commissioned even before the first one was shown.
The windmill that Jonathan Creek lives in, is open to the public. It's in the town of Shipley, West Sussex, around 6 or 7 miles South of Horsham, England.
In the very first episode, the character of Adam Klaus was played by Anthony Head. Although intended to be in every episode, the character was never seen in the rest of the first series. For the second series and beyond, Stuart Milligan played the role due to Head's involvement in "Buffy the Vampire Slayer" (1997).
Adam Klaus was originally to have been called Adam Faust, but this had to be changed when checks by the BBC's Legal Department revealed that there was a real-life magician with this name.