| Type: | town |
| County: | Hunedoara |
| Official Name: | Geoagiu |
| Leader Name: | Vasile Cărăguț[1] |
| Leader Party: | PSD |
| Term: | 2020 - 2024 |
| Coordinates: | 45.92°N 23.2°W |
| Elevation: | 217 |
| Area Total: | 155.69 |
| Population Total: | auto |
| Postal Code: | 335400 |
| Area Code: | (+40) 02 54 |
Geoagiu (Hungarian: Algyógy, German: Gergesdorf) is a town in Hunedoara County, in the historical region of Transylvania, Romania, located on the Mureș River at an altitude of above sea level. The river with the same name (Geoagiu) flows in this place into the Mureș.
It administers ten villages: Aurel Vlaicu (until 1925 Binținți; Bencenc), Băcâia (Bakonya), Bozeș (Bózes), Cigmău (Csigmó), Gelmar (Gyalmár), Geoagiu-Băi (Feredőgyógy), Homorod (Homoród), Mermezeu-Văleni (Nyírmező), Renghet (Renget), and Văleni (Valény).
The first settlements in the area can be found in the time of the Dacians, in the 1st century BC, as shown by archeological discoveries. After the Roman conquest, the Romans built the fort of Germisara in the 2nd century, however, it kept the original Dacian name.
The name of Germisara meant "hot water" (germi = "heat", sara = "waterfall") and it showed that the Dacians already knew of the thermal springs of the area. Another opinion that the name came from the Hungarian name of the Geoagiu River (Gyógy), which means "curative". But more probably, the name is coming from the Hungarian word dió (nut as fruit) with the suffix -d, so, after the first documentary citation, "villa Gyog" from 1291 appeared as Dyod és Dyog (1397), Aldyogh (1407), Algyogh (1412), Aldyod (1439), Alsodyod alio nomine Alsoffalwa (around 1444).
The first documentary citation of Geoagiu (it was written as "villa Gyog") was in the year 1291, when it was used as a land in the vicinity of Binținți (now the village Aurel Vlaicu).
There are remains of the old Roman road from Geoagiu to Geoagiu Băi made of flat stones.