| Official Name: | São João da Fronteira |
| Settlement Type: | Municipality |
| Pushpin Map: | Brazil |
| Pushpin Map Caption: | Location in Brazil |
| Coordinates: | -3.9556°N -41.2575°W |
| Subdivision Type: | Country |
| Subdivision Name: | Brazil |
| Subdivision Type1: | Region |
| Subdivision Name1: | Northeast |
| Subdivision Type2: | State |
| Subdivision Name2: | Piauí |
| Subdivision Type3: | Mesoregion |
| Subdivision Type4: | Microregion |
| Subdivision Name4: | Litoral Piauiense |
| Subdivision Type5: | Metrop. region |
| Leader Title: | Mayor |
| Area Total Km2: | 764.86 |
| Population Total: | 6,064 |
| Population As Of: | 2020 [1] |
| Population Density Km2: | auto |
| Timezone1: | BRT |
| Utc Offset1: | -3 |
| Postal Code Type: | Postal code |
| Area Code Type: | Area code |
São João da Fronteira (Portuguese meaning "Saint John of the frontier") is a municipality in the western part of the state of Piauí in Brazil. The population is 6,064 (2020 est.) in an area of 764.86 km².[2] The elevation is 458 m.
The municipality contains part of the Serra da Ibiapaba Environmental Protection Area, created in 1996.