Sorry, but I have to say Icewing is partially incorrect. He got the first part right... US Army 1st Kentucky Regiment. But the emblem's background being crosshatched lines with acorns inside the squares formed by the lines means your US Army collar-insignia disc dates from 1921 to 1937. It is referred to as a "Type 2" disc here: Dating Metallic Insignia: Collar Disks
Scroll down that webpage to the Type 2 discs, and look very closely at the "crosshatched lines background" discs. I can't be absolutely certain from your photo whether the background shows acorns, or shields/dots, but what I'm seeing looks more like acorns.