Also came from king of Prussia, valley forge area in pa

Not much because of the shipping costs.

It's worth what someone will pay...
I wonder if ti is really a mill stone because I see none of the srtiations that guide the grain to the center....but maybe the other side is striated.
I suggest you contact mainemillstones.com they sell new and "historic" millstones.
If it is a millstone and has been dressed it should be worth about $500 maybe more.

Lazy...you don't ship a millstone!

That's a Grindstone, likely from a 19th century water-powered factory somewhere. You can tell it's not a mill stone for the reason noted above by lindac92, but with a 36" diameter it is nonetheless a desirable piece of garden decor.

It will never bring the kind of money that a grindstone that large would (which could be in the neighborhood of a couple thousand dollars) but it will sell so long as the portion now buried in the soil is all there, if for no other reason than that the most obvious use for a stone this size is as part of a fountain, probably the base, which means it will placed horizontally, flat on the ground, instead of vertically, with some part of it buried.

And lindac92, sorry, but these things are shipped here, there, and everywhere. Real shippers actually prefer them because compared, say, to a much larger piece of furniture or even a nice oil painting of similar size to it, the stone weighs so much. All truck shipping is priced according to a combination of volume and weight. This little puppy probably weighs about 275 pounds but takes up less than five cubic feet, a shipper's dream, whereas if I were to load just four of them into my van to take to a show, technically, legally (and intelligently) I wouldn't have room for anything else.

I will routinely take as much as six or seven hundred pounds of stone this or stone that to a show in the Spring ("garden time") but I have to place them directly over the rear axle and then be very careful of how much the rest of the load weighs and where to place it. Yes, shipping by common carrier seems expensive, but it's a lot more economical than it would be for me to bring it to you (and then return home empty) or for you to maybe come visit family in the northeast for a couple of weeks, traveling real light, then stopping by to pick it up and carry it back home.

I believe it is a grind-stone, not a mill-stone, for the same reasons stated above. It is a big, heavy one likely too large for a foot pedal powered wheel. It probably was in a water powered mill and used for heavy duty grinding.

It would be suitable for putting an edge on an axe or dressing off the peened edges that develop on the heads of wedges and chisels.

Considering this one, and that it's made for a grown man to use ... you have a grindstone used for a bit more than sharpening knives. Perhaps used for sharpening mowing machine blades, scythes and other agricultural equipment.

Blacksmiths also use large grindstones.

Still interesting, but not all round rocks are "mill stones".