Nahavand County () is in Hamadan province, Iran. Its capital is the city of Nahavand.
At the time of the 2006 National Census, the county's population was 178,683 in 46,283 households. The following census in 2011 counted 181,711 people in 53,821 households. The 2016 census measured the population of the county as 178,787 in 55,542 households.
Nahavand County's population history and administrative structure over three consecutive censuses are shown in the following table.