Damghan County () is in Semnan province, Iran. Its capital is the city of Damghan.
The area suffered damage in the 856 Damghan earthquake.
The village of Kalateh was converted to a city in 2011.
At the time of the 2006 National Census, the county's population was 81,993 in 23,020 households. The following census in 2011 counted 86,908 people in 25,554 households. The 2016 census measured the population of the county as 94,190 in 30,296 households.
Damghan County's population history and administrative structure over three consecutive censuses are shown in the following table.
The Ali Spring (Cheshmeh-ye Ali) is in Damghan County (not be confused with the Cheshmeh-ye Ali in Ray, southern Tehran). Amirabad District forms the major part of the county. The three cities are Damghan, Dibaj and Amiriyeh.
Other important villages in the county are: Mehmandust, Naimabad, Tazareh, Tuyeh, and Darvar, Qusheh, Hasanabad, and Rashm.
Main Tehran-Mashhad railway is 5 km south of Damghan. Damghan is alongside of Tehran-Mashhad Highway. From south there is main road to Isfahan and Yazd, and northward from Ali Spring (Cheshmeh Ali) & Tuyeh Darvar to Sari and through Dibaj to Behshahr & Gorgan.
Damghan city itself has many ancient and historical places. However outside the city also there are some attractions like: