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.
As you can see, there are plenty of suppliers based in the US, the most prolific of which produce glass and processors for iOS devices. [China File]