Available info indicates that the A8 is fabbed on a 20nm process by both Samsung and TSMC [1]. For Samsung, that would indicate production in either the US or South Korea [2]; for TSMC, that would indicate production is in Taiwan [3].
[1] http://recode.net/2014/09/23/teardown-shows-apples-iphone-6-...
[2] http://www.samsung.com/global/business/semiconductor/foundry...
[3] http://www.kitguru.net/components/graphic-cards/anton-shilov...