https://en.wikipedia.org/wiki/Cinco_de_Mayo
“Celebrations began in California, where they have been observed annually since 1863. The day gained nationwide popularity beyond those of Mexican-American heritage in the 1980s due to advertising campaigns by beer, wine, and tequila companies; today, Cinco de Mayo generates beer sales on par with the Super Bowl.”
In my East Coast experience, I never heard of “Cinco de Mayo” until c.2000.