The commitment seeks to strengthen economic growth in the region and discourage illegal immigration.
The United States pledged $5.8 billion in aid Tuesday for strengthening government and economic development in Central America, and another $4.8 billion in development aid for southern Mexico.
The US aid aims to promote better security conditions and job opportunities as part of a regional plan to allow Central Americans to remain in their countries and not have to emigrate.
The plan was announced in a joint US-Mexican statement released by the State Department and read aloud by Mexican Foreign Relations Secretary Marcelo Ebrard in the Mexican capital.
"In sum I think this is good news, very good news for Mexico," Ebrard said.
"The commitments established here signify more than doubling foreign investment in southern Mexico starting in 2019," he added.
Southern states like Chiapas and Oaxaca are home to many of Mexico's poorest communities. President Andres Manuel Lopez Obrador, who took office December 1, has sought to make development in that region a priority, including plans for a "Mayan train" stretching from touristy parts of the Yucatan Peninsula down to Chiapas.
It was unclear if Mexico would give anything in return.
A planned announcement about Mexico's migration policy was postponed until Wednesday.
The United States has reportedly wanted Mexico to allow migrants seeking asylum in the United States to remain in Mexico while their applications are processed.