Inside

Underside of shelf

Under bottom

Bottom side

Nails from trim

Hard to say, because people working with old-style tools can make something just like that today.

I think you have the top half of a home-built hutch or jelly cupboard. It could be interesting and useful when cleaned up.

So many of those were homemade, like already said, so there weren't any 'rules' to follow. One just made them to suit their needs. I have a couple myself, one with legs like yours and who knows if it's been modified. It's neat and I like it. Certainly rustic and no reason to believe it's not old. I find those square nails all over my house in odd places, but then again it's a very old house.

Those square nails are old, possibly before1900. The cabinet appears to be home built. It would have sat on a cabinet or table who's top was about 30 inches above the floor. Farmers wives referred to these as a "kitchen cabinet". The part you have would have sat about 10 inches above the table surface so that the entire table top was available for use and to elevate the door above the table top, otherwise, the door would sweep the table.

A clue is the door construction. It screams home built. I don't see any plywood. Every piece appears to be solid wood and no veneer

The other possibility is it is simply a utility cabinet and what you see is all that it ever was..