Do you need a cdl to drive a 24 ft boxed truck?

You would if one or more of the following circumstances applied:

• It is a vehicle with a Gross Vehicle Weight Rating of more than 26,000 lbs., which does not fall under a type exempted from CDL requirements (emergency vehicle, military vehicle in current military service, recreational vehicle, or registered farm vehicle).
• It is a vehicle which, while pulling a trailer, has a Gross Combination Weght Rating (weight rating of the truck plus the weight rating of the trailer) in excess of 26,000 lbs., which does not fall under a type exempted from CDL requirements (emergency vehicle, military vehicle, recreational vehicle, or registered farm vehicle)
• It is a vehicle, of any weight rating, which is carrying a quantity of hazardous materials that requires hazmat placards to be displayed.

Otherwise, no.