Nahavand County is in Hamadan province, Iran. Its capital is the city of Nahavand.

Hamadan province is an Iranian province located in the Zagros Mountains. Its capital is the city of Hamadan. The province covers an area of 19,546 km2. According to the National Census held in 2006, Hamadan had a population of 1,674,595 in 427,675 households. The following census in 2011 counted 1,758,268 people in 506,191 households. In 2014, Hamadan province was placed in Region 4. The latest census in 2016 revealed a slight decrease in the population to 1,738,234 in 538,803 households.