Definitely an early design, as Huntsman53 has suggested it's likely pre-1800.
Hand decorated on the front... to me, the 'Eagle' looks to be Mexican or Spanish in origin.
Could this be a rather crude version of the eagle design from a US Revolutionary War button?
I looked more closely at the bird and it appears to be more likely a Pelican than an Eagle. It has the wing characteristics of a Pelican and what appears to be webbed feet but the problem is, that it's neck and head appear to have been mostly destroyed by corrosion. I still believe it is old but maybe not as old as I thought and was likely hand made. Louisiana used a Pelican on their' Confederate buttons and wonder if it is a hand made version (see the 1st link below to view a rare Charles Bellenot Pelican Button made in New Orleans)(the 2nd link below is to TNET member 7539's find of a 3rd Louisiana Infantry Coat Button). However, it could be button related to sea life aboard a ship and if so, it is possible that it does date back to the Colonial period.