Karaj County (Persian: شهرستان کرج) is a county in Alborz Province in Iran.
The capital of the county is Karaj.
At the 2006 census, the county's population was 1,709,481, in 472,365 families. The county is subdivided into two districts: the Central District and Asara District. The county has seven cities: Karaj, Asara, Garmdarreh, Kamal Shahr, Mahdasht, Meshkin Dasht, and Mohammadshahr.