Grandfathers Davenport desk

I would like to get a little information/history on my Grandfathers old walnut Davenport Desk.

My Grandfather owned a meat packing company in Springfield, IL 100+ years ago. My mother (65 years old) told me that my Grandfather traded meat for this desk approximately 25 years+ before she was born, so it is at least 90 years old!

The desk is handmade and in pretty good shape to be as old as it is. The dimensions are 26.5"wide x 20.5" deep x 31" tall (from the) the shelf adds an additional 18" to the total height. Inside of the desk the dimensions are: 23 1/4 wide x 14 deep with 3 spaces for storage.

Can anyone give me a little background on this desk? How old it might be and if its valuable?

Thanks in advance!