Esfarayen County (Persian: شهرستان اسفراین) is in North Khorasan province, Iran.

It was only Esfarayen that resisted the flood of violence that swept away the ancient and sedentary Persian-speaking farmers and townsfolk of northern Khorasan, starting with the Mongol invasion, the coming of destructive tribes, and finally the massive murder and depopulation of northern Khorasan in the 18th and 19th centuries by the hands of Turkmen raiders and slave catchers.

Khorasani Persians were found in great numbers at the slave markets of Khiva and Kashgar in China in the late 19th century, being sold by the Turkmens.

Esfarayen preserves what the entire northwestern Khorasan (including the whole southern half of Turkmenistan) must have looked like before the avalanche of the Turkic nomadic invasion began in the 11th century.

[2] Esfarayen County's population history and administrative structure over three consecutive censuses are shown in the following table.