1/2″ holes in my lawn in virginia
Holes are burrowed into soil. Most are topped with what is probably the soil that is excavated and is totally covering the hole. These are in my lawn. Sometimes I'll find some with no soil on top. I've dug into them to find nothing. Maybe I didn't go deep enough. It's not earthworms, as they leave a specific dirt casing. These holes have loosely piled dirt covering them. There are literally hundreds of them in a 100' x 50' area.
This could be voles, moles, rats or chipmunks.
I found a few links for you that may help determine the critter.