America's first President issued the proclamation way back in October 1798, designating a Thursday in late November as the first official Thanksgiving holiday.

The founding father's handwritten proclamation, complete with his signature at the bottom, is going up for sale through Moments In Time ... with a whopping $15 million price tag.

The historically significant document is being sold by a private collector, and its value has risen exponentially over the years as it's changed hands.

When the piece first hit the open market in 1977, it sold for $3,000 ... and when it was on the market again almost 7 years ago, it sold for $6.5 million.

Now it's going for $15 million ... which is an awful lot of Thanksgiving dinners.