Fereydunkenar County () is in Mazandaran province, Iran. Its capital is the city of Fereydunkenar.
In 2007, Fereydunkenar District was separated from Babolsar County in the establishment of Fereydunkenar County, which was divided into two districts of two rural districts each, with Fereydunkenar as its capital and only city at the time. The village of Astaneh-ye Sara was converted to a city in 2022.
At the time of the 2011 National Census, the county's population was 57,980 people in 17,574 households. The 2016 census measured the population of the county as 60,031 in 20,066 households.
Fereydunkenar County's population history and administrative structure over two consecutive censuses are shown in the following table.