The municipality of Zagorje ob Sava lies in the heart of Slovenia. It covers an area of 147 square kilometers, on which about 16,500 inhabitants live (16,439 inhabitants on 01/01/2020, of which 8,198 are men and 8,241 are women). The population density is 112 inhabitants per square kilometer.
The municipality is divided into 13 local communities (Jože Marn, Rudnik - Toplice, Franc Farčnik, Čemšenik, Izlake, Kisovec - Loke, Kotredež, Mlinše - Kolovrat, Podkum, Ravenska vas, Šentlambert, Tirna, Šentgotard) which include 78 settlements.
The altitude of Zagorje ob Sava is 224 meters, and the highest settlement in the municipality is Mali Kum with 820 meters above sea level. Zagorje ob Sava, Loke – Kisovec and Izlake are the largest settlements in the municipality, while the smallest settlement is Druzina. Among the oldest settlements are Tirna, Zagorje ob Sava, Izlake and Čemšenik.

Neighboring municipalities are: Trbovlje, Radeče, Litija, Moravče, Lukovica, Kamnik, Vransko, Tabor. The municipalities of Zagorje ob Savi, Litija, Trbovlje and Hrastnik make up the statistical region of Zasava. The municipality has three main primary schools, five branch schools, a school with an adapted program, a secondary school and a music school.

The town of Zagorje ob Savi is 52 km from Ljubljana, 36 km from Celje, 6 km from Trbovelj, 17 km from Litijje and 22 km from the Geometric Center of Slovenia GEOSS.

Velika or Čemšeniška planina is the highest peak in the municipality at 1,205 m above sea level (Črni vrh 1,205 m). The maximum depth before the mine was closed was 262 m. The longest stream in the municipality is Medija, and the Sava river flows through the municipality.

Zagorje ob Sava lies on the 15th meridian of east longitude, and the European footpath E6 touches the municipality of Zagorje near Trojane.