Indigenous languages of the Americas are spoken by indigenous peoples from Alaska to the southern tip of South America, encompassing the land masses that constitute the Americas. These indigenous languages consist of dozens of distinct language families, as well as many language isolates (natural language with no demonstrable "genetic" relationship with other languages) and unclassified languages. According to UNESCO, most of the indigenous American languages are critically endangered, and many are already extinct.

The most widely spoken indigenous languages are:

Quechua - with about 8 million speakers, primarily in the Andean region of South America.

Mayan languages - with about 6 million speakers, primarily in Mexico and Guatemala.

Guarani - with about 5 million speakers in Paraguay and surrounding areas of Argentina, Brazil and Bolivia.

Note that in several of these cases, a "language" may actually include several related, but not identical, languages. For example, Quechua speakers in Ecuador and Bolivia really can not understand each other (although both of them may be able to understand an intermediate form of their language.) There are also dozens of different Mayan languages, which could be listed separately. However, since these languages are not recorded separately on the census records of Central and South American countries, it becomes very difficult to compare the total estimated population of speakers at a finer level than "Quechua" or "Mayan."

More Info: en.wikipedia.org