The season 7 episode "Every Man's Family" was meant as the pilot for a proposed spinoff for the character of Bubba Skinner. The network did not have any available slots at the time it was first broadcast and In the Heat of the Night ended soon after, so the spinoff never materialized. It would have been set in Atlanta.
After the series ended, the house which served as Virgil Tibbs' home sat empty for a few years, before being divided up and used as office space.
Carroll O'Connor wrote several scripts under the pseudonym, Matt Harris, for the show and two "In the Heat of the Night" movies. He worked under the pseudonym concerned that his scripts would not be received well by television critics.
The season after Howard E. Rollins Jr. left the cast, he did return for several guest appearances. However, Anne-Marie Johnson (who played Althea) chose to join the cast of "In Living Color. Her absence was explained by having Althea & Virgil separate because of her having emotional problems stemming not only from her rape, but the stress of her being married to a policeman.
The first season was filmed in Hammond, Louisiana, before moving to Conyers and Covington, Georgia for the rest of the series. That would explain why the 'look' of Sparta changed after season one.