San Mateo is a proper noun referring to a city in California and a common surname. It is pronounced as two syllables in English, typically with a stress on the second word when used in full as a place name (SAN ma-TE-o) or on the final syllable in some Spanish-influenced contexts. The pronunciation often features a soft, unstressed “a” and a clear “te” syllable, with attention to vowel quality and final vowel.
Full pronunciation guide