Kumarsain (English: /kumærsæɪn/; Hindi: [kʊmaɾsain] ⓘ), also known as Kumharsain, is a town in Shimla District in the Indian state of Himachal Pradesh.

It is situated above the Satluj river in the North-West Himalayas, about 80 km from Shimla towards interior ranges.

Kumarsain has many villages within its boundary namely Mateyog, Damali, Lathi, Bharara, Bai and Dethal.

Tourist attractions around Kumarsain include Narkanda, Kotgarh-Thanedhar, Hatu Peak, Tani Jubbar Lake, Derthu Mata Temple Kumarsain was a Constituency of Himachal Pradesh Legislative Assembly and had a separate election seat until 2008 delimitation, when it was merged with Theog Assembly constituency.

Veteran Congress Minister Vidya Stokes was elected 2 times as MLA in 2003 [4] and 2007 [5] from Kumarsain Assembly Constituency.