| Settlement Type: | District |
| Official Name: | Once de Septiembre |
| Pushpin Map: | Argentina Greater Buenos Aires |
| Pushpin Label Position: | bottom |
| Pushpin Map Caption: | Location in Greater Buenos Aires |
| Pushpin Mapsize: | 240 |
| Subdivision Type: | Country |
| Subdivision Type1: | Province |
| Subdivision Name1: | Buenos Aires |
| Subdivision Type2: | Partido |
| Subdivision Name2: | Tres de Febrero |
| Established Title: | Founded |
| Population Total: | 4,355 |
| Coordinates: | -34.6°N -89°W |
| Elevation M: | 24 |
| Postal Code Type: | CPA Base |
| Postal Code: | B 1657 |
| Area Code: | +54 11 |
Once de Septiembre is a town in Tres de Febrero Partido of Buenos Aires Province, Argentina. It is located in the Greater Buenos Aires urban agglomeration. The name is often spelt "Once de Setiembre"[1] (both spellings are correct) or "11 de Setiembre/Septiembre".
The town is named for the September 11, 1852, rebellion of Buenos Aires against the Federal government of General Justo José de Urquiza.[2]
With only 4,355 inhabitants, Once de Septiembre is the least populous district in Tres de Febrero Partido.