Yep, it is for the most part only celebrated in Puebla since it was their militia who defeated the French there...though Napolean just sent more troops and eventually occupied Mexico city (for 3 years) until his cousin (Maximillian) was executed by the Mexicans in 1867.

May 1st was a major holiday in the Soviet Union and other communist countries so we kind of ignore that here in favor of May 5th.