Grodzisk municipality is located in the eastern part of the country, in the southern part of Podlaskie province. The municipality, as well as the entire district, lies within the Drohiczyn Highlands, which are part of the Polish part of the Podlasie-Belarusian Highlands.

Flowing waters constitute the catchment area of the Bug River flowing into the Vistula and the Baltic. The territory of the municipality is located in the southern part of the area referred to as the Green Lungs of Poland. The area of the municipality is 20321 km². The population of the municipality is 4342 (the village of Grodzisk has 564 people). The municipality has 42 villages.

The municipality of Grodzisk is located in the northwestern part of Siemiatycze County and neighbors:

• On the western side with the municipalities: Ciechanowiec and Perlejewo,
• from the north with the municipalities: Rudka, Brańsk and Boćki,
• From the east with the municipality: Dziadkowice,
• On the south side with the municipalities: Drohiczyn and Siemiatycze.

The Grodzisk municipality has an agricultural character. Its area is dominated by individual farms engaged in grain cultivation. The production of potatoes, fodder and industrial crops and vegetables plays a smaller role. The farms also raise cattle, mainly dairy, and pigs. There is a lack of large industry in the municipality, with only small business establishments.