Garett Maggart was cast as Blair before Jim's role was assigned. He screen tested with a few of the Jims in the running but once Richard Burgi came on the scene it was pretty much decided. They had instant chemistry.
The series was originally intended to be set in Seattle, but city officials asked the producers to change so as to not give their town a reputation as a crime scene. Thus, the fictional city of Cascade came into being. The only remnant of Seattle was an undeleted reference to the Seattle Supersonics in the pilot episode. The Cascade basketball team became the Jaguars in later episodes.