According to the Palestinian Central Bureau of Statistics (PCBS), the town had a population of 2,251 inhabitants in 2017.

"[5] Qusin, like the rest of Palestine, was incorporated into the Ottoman Empire in 1517, and in the census of 1596 it was a part of the nahiya ("subdistrict") of Jabal Sami which was under the administration of the liwa ("district") of Nablus.

The villagers paid a fixed tax-rate of 33,3% on agricultural products, such as wheat, barley, summer crops, beehives and/or goats, in addition to occasional revenues and a customary tax for people of Nablus area; a total of 6,300 akçe.

[6] In 1870/1871 (1288 AH), an Ottoman census listed the village in the nahiya (sub-district) of Wadi al-Sha'ir.

[7] In 1882, in the PEF's Survey of Western Palestine, Kusein was described as: "A village on the side of a ridge, apparently supplied by the water of the valley on the north, which has a flowing stream.