Hello!
An inch long would fit the European Chafer as a grub if it was mature. Some chafers such as the June Bug I think will be similar to our May Bug Melolontha melolontha, it takes up to 4 years to emerge with the almost mature beetle staying in the ground over the last winter. They start small and grow so size isn't always an indication but can cut out the smaller ones at maturity.
http://msue.anr.msu.edu/resour...
I searched your location and found a few which are present in your area, this type of beetle larvae feed on grass roots but some also feed on other roots such as trees, shrubs and other plants. Having found them under rocks is odd, are there lots of roots growing under the rocks?
European chafer, May and June beetles, Japanese beetle, Asiatic beetle, Northern and Southern Masked Chafer, Black Turfgrass Ataenius, Green June beetle and Oriental beetle
http://springfield-mo.weedmanu...
A list of different possible species ..
https://en.wikipedia.org/wiki/...
Beetles can fly albeit not very well, so even if you haven't seen a particular species they can easily get there. May or June Bugs fly at night, attracted to light so you might not see them.
Some info ..
http://entnemdept.ifas.ufl.edu...
http://turf.uark.edu/turfhelp/...
Unless you can get a good shot of the raster which you have smashter then you won't be able to tell what it is, even if you could get a good shot it would be difficult to tell without a good microscope and expert knowledge.
https://springfieldmo.gov/Docu...
