Military button found in Kentucky creek

I found this military button about 10 years ago in a creek in Kentucky , my dogs and I hike on a regular basis. I always wondered how the button ended up in the creek? It is approximately 7/8” wide. The back is marked with the name Horstmann, Phila. It’s made of brass I believe. Does anyone have any ideas, when this military button was produced? Any comments would be appreciated.