Tehran Province sits on the southern slopes of the Alborz mountain range, extending southward into the central desert basin of Iran. It is bordered by Mazandaran Province to the north, Qom Province to the south, Semnan Province to the east, and Alborz Province to the west. This positioning gives the province a distinct dual geography: alpine and heavily folded terrain in the north, and relatively flat, arid plains in the south.
The province's hydrology is primarily driven by mountain runoff. Major rivers include the Karaj River (which originates in the neighboring Alborz province but heavily impacts Tehran's water supply) and the Jajrood River in the east, which feeds the Latyan Dam. Forests are generally sparse and confined to protected mountain valleys, while the southern reaches of the province edge into semi-desert landscapes.
Due to its location at the foothills of the Alborz mountains, Tehran Province sits on several major active fault lines (including the Mosha and North Tehran faults), making it highly susceptible to seismic activity.