| San Agustín del Guadalix | |
| Settlement Type: | Municipality |
| Pushpin Map: | Spain |
| Pushpin Map Caption: | Location in Spain. |
| Subdivision Type: | Country |
| Subdivision Name: |  Spain |
| Subdivision Type1: | Autonomous community |
| Subdivision Name1: | Community of Madrid |
| Subdivision Type2: | Province |
| Subdivision Name2: | Madrid |
| Subdivision Type3: | Comarca |
| Subdivision Name3: | Cuenca del Medio Jarama |
| Leader Title: | Mayor |
| Leader Name: | Juan Francisco Figueroa Collado |
| Area Total Km2: | 38.3 |
| Population Demonym: | Olmedeños |
| Population Density Km2: | auto |
| Population Blank1 Title: | Ethnicities |
| Utc Offset: | +1 |
| Utc Offset Dst: | +2 |
| Coordinates: | 40.6781°N -3.615°W |
| Elevation M: | 684 |
San Agustín del Guadalix is a Spanish town located north of the Comunidad de Madrid, near to Sierra de Guadarrama.
It is bordered by Pedrezuela to the north, the municipalities of El Molar and Algete to the east and Colmenar Viejo to the south and west.
The origin of the town is obscure, but it appears that it was settled by the Iberians in the pre-Christian era. Proximity to Madrid has made it popular as a commuter base, resulting on its population more than tripling from 2,459 inhabitants in the late 20th century to over 9,000 in 2006. https://web.archive.org/web/20070315163239/http://www.madrid.org/iestadis/fijas/estructu/general/otros/descarga/sanagustin05.pdf In 2022 it had a population of 13,608.[1] This has substantially changed the face of the town, resulting in blocks of flats replacing the older two-storey buildings as the preferred means of accommodation. Furthermore, the traditional agriculture and livestock industries have been superseded by heavy industry.
The town's main festival takes place the third Sunday of May in honour of the Virgin of Navalazarza.