Sabzevar County () is in Razavi Khorasan province, Iran. Its capital is the city of Sabzevar.
In 2007, Joghatai and Joveyn Districts were separated from the county in the establishment of Joghatai and Joveyn Counties, respectively. In 2010, Khoshab District was likewise separated to establish Khoshab County.
In 2012, Davarzan District was separated in the establishment of Davarzan County. In 2020, Sheshtamad District was separated to establish Sheshtamad County.
At the time of the 2006 National Census, the county's population was 429,187, in 116,891 households. The following census in 2011 counted 319,893 people in 98,581 households, The 2016 census measured the population of the county as 306,310 in 95,553 households.
Sabzevar County's population history and administrative structure over three consecutive censuses are shown in the following table.