| San Marcos | |
| Settlement Type: | Municipality |
| Mapsize: | 250px |
| Pushpin Map: | Mexico |
| Pushpin Label Position: | above |
| Pushpin Mapsize: | 300 |
| Pushpin Map Caption: | Location in Mexico |
| Subdivision Type: | Country |
| Subdivision Name: |  Mexico |
| Subdivision Type1: | State |
| Subdivision Name1: | Guerrero |
| Subdivision Type2: | Municipal seat |
| Subdivision Name2: | San Marcos |
| Established Title2: | Founded |
| Established Date2: | 28 September 1885 |
| Area Total Km2: | 960.7 |
| Population As Of: | 2005 |
| Population Total: | 44,959 |
| Population Blank1 Title: | Ethnicities |
| Population Blank2 Title: | Religions |
| Coordinates: | 17.4167°N -119°W |
| Elevation M: | 30 |
San Marcos is a municipality in the Mexican state of Guerrero. Its municipal seat is the town of San Marcos.
The municipality of San Marcos covers an area of 960.7 km² and is home to approximately 50 000 inhabitants. Ethnically, the population is mainly indigenous with a considerable mixing with African and to a lesser extent, European settlers, making most sanmarqueños Zambos. It comprises 138 villages and towns, examples of which include El Cortes, Las Vigas, El Cerro, Vista Hermosa, Tecomate de Pesqueria, Monte Alto, Santo Domingo, Las Ramaditas and others. Many sanmarqueños have migrated to various places in the United States, including the San Francisco Bay Area (mainly Oakland), Southern California (mainly Los Angeles, Santa Ana, and San Diego), Arizona, Chicago Illinois, Atlanta Georgia, Winston Salem North Carolina, South Florida, Washington State, as well as Houston and Dallas Texas.