'non-Mexican' is formed in English by adding the prefix 'non-' (meaning 'not') to 'Mexican', which refers to someone or something from Mexico.

The prefix 'non-' has been used in English since the Middle English period to indicate negation, and 'Mexican' comes from 'Mexico', the country name, plus the English suffix '-an'.

Initially, it simply meant 'not Mexican', and this meaning has remained unchanged.