All I could find were articles from 2013 that indicate many were assembled earlier in Fremont, California at Quanta facilities (and they have facilities in Tennessee but maybe nothing to do with this), and later to be assembled in Texas, including components made in Illinois and Florida, and relying on equipment produced in Kentucky and Michigan. Tim Cook indicated in senate hearings in May 2013 that components for newer Macs would be sourced from Arizona, Texas, Illinois, Florida and Kentucky. So this sounds like a good bet more than 90% of components are made here.
Now they’re assembled at plants in Elk Grove, CA, about fifteen miles from where I live, and in Austin, Texas.