Knoxville's a great city and if I didn't live in Lexington, I would live there. As far as crime, Im not too familiar with the area, my family lives there and I always heard about staying away from Mechanicsville and Lonsdale area. And yes, Knoxville has or did have gang activity.
Knoxville has 130 registered sex offenders.
You can see whether they are in the places you plan to visit by going to:
Knoxville is well above average in the number of criminal activites within the metropolitan area.
Petty Theft is by far the most prevelant problem, followed by Auto Theft and Burglary.
So you need to make sure that car doors and motel room doors are secured.
Keep valuables in the motel safe when touring the area. Use a money belt so that your wallet contains a minimum of valuable cash or credit cards.
Certain areas are not very safe late at night within the city limits. Your hotel staff will be able to indicate which regions are dangerous.
Use caution and common sense and you can have a safe vacation in Knoxville.