I found this perfectly round stone when digging in my yard today in Cumberland Maryland. My home was built in 1920 and the home adjacent was built in 1910. The land was once farm land. There is no streams or cricks near by. I posted it with a marble to show shape and size
I noticed this is your very first post - so, Welcome Aboard Jenn! Take a look at Sub-Forums: Maryland for information (i.e., clubs, etc.) directly related to your state.
Are you sure it is stone? It could be a musket ball. Lead bullets get a white chalky patina on them when they've been in the ground 100+ years.
I give Civil War living history presentations to 4th graders and I let them hold CW bullets I've dug. Every time one of them will remark - "I didn't know they were made of stone!"