This township lies in the west of the province. To its north lies Firooz Kooh and Damavand and to its western limits are Varamin and Qom. In the south lies the desert region of Esfahan province and the Salt Lake to the west. The villages of this township are fed by the minor tributaries of the Hableh River. Garmsar is situated on the plains 107 km. from Tehran and the railway line of Tehran - Gorgan and Tehran - Mashad branches off at this point. This city, having a quaint background, was one of the districts of Khar in the past and in the year 1959 become a township.
The Hablehrood river originating from Dalichai-Firouzkooh flows to the plateau of Garmsar. Its water is extensively used for agriculture. Since salt water mixes with Hablehrood before its arrival to the city, the water is not fit for drinking. Hablehrood is the only permanent river in Semnan province. Thanks to the water provided by Hablehrood, people in Garmsar grow wheat, barley, cotton and yellow melon. Garmsar is known across Iran for its sweet and crispy yellow melons.
The traditional cuisine of the city is called Tahchin. It differs from the classic Tahchin common in other cities. Tahchin is a tasty and fragrant rice-based food where marinated raw meat is slowly cooked inside the rice over a low flame for several hours.