That's an old lathing (carpenter's) hatchet. Hard to pin an exact year but it's probably mid 1800s - early 1900s.
You have me curious if it has any markings! I played around with your picture and tried to enhance. If you zoom real far it looks like there may be an "E" in there. TrueTemper sometimes place their mark in that area. A little steel wool will take just the surface rust off. Who knows - It could be just the way it rusted. To the pic view the best it has to be opened in a new window for full zoom.