Lenjan County (Persian: شهرستان لنجان) is a county in Isfahan Province in Iran. The capital of the county is Zarrin Shahr (Riz-e Lenjan). Lenjan County is also the location of Isfahan Steel Mill. It is located on the banks of the Zayandeh River, which the largest river in Isfahan Province. Farming is an important source of income, and the most important product in Lenjan is rice. At the 2006 census, the county's population was 225,559, in 58,232 families. The county is subdivided into three districts: the Central District, Fuladshahr District and Bagh-e Bahadoran District. The county has eight cities: Chamgardan, Charmahin, Bagh-e Bahadoran, Zarrin Shahr, Sedeh Lenjan, Varnamkhast, Fuladshahr, and Zayandeh Rud.
The main route passing through the county is Road 51, connecting population centres to Isfahan and Shahrekord.
Falavarjan County has its own Transit Bus system named Lenjan County Mass Transit Organization.