Where are the Aztecs now?

They live in Mexico. There are still more than a million speakers of Nahuatl (the language of the Aztecs). Most Mexicans have some Amerindian blood from the Aztecs and other native tribes such as the Maya, the Tlaxcala, the Apache, the Comanche, the Navajo etc. The Aztecs although they were defeated are not extinct, this is a common misconception.