Large Antique Roll Top Desk - Tell City Co.

My parents bought this beautiful roll top desk about 50 yrs ago. It has a paper under the desk top that says Tell City Desk Co. #81 There is little hardware, a couple of screws and the lock. The wood is put together by interlocking- a picture of the side of a drawer is included. Also,  seen is the inside of a drawer. Thin wood slats work as dividers. The bottoms are thin wood also. On either side of the center open area are carved areas for probably pens. and also there are 2 little drawers that have curved bottoms. I really would like to know how old this desk is and how much its worth. I don't know if I want to sell it. Thanks so much for your help.