This map, put together by China File, plots all of the publicly available suppliers who fuel Apple's production lines. While the majority are found in Asia, it's interesting to see that the rest of world represents, too.
Each point on the interactive map represents an individual supplier, provided with complete context—from Analog Devices in Limerick, Ireland, to Arvato Digital in Smithfield, Australia. Explore the zoomable, clickable version of the map here.
There are, as you can see, plenty of suppliers based in the US, the most important—or at least, prolific—of which produce glass and processors for iOS devices. [China File]