At the 2011 census, its population was 373,987. Sanandaj is the twenty-third largest city in Iran. Until the 17th century it was only a small village, when the governor of the region, Suleyman Khan Ardalan, built (or renovated) a fortress there, known as “Sena Dezh”, which gave the town its Persian name. Some sources date the origin of the fortress to the period of Abbasid rule (750–1258)
The suffix Diz means castle and also thief in the Iranian languages. There are four Kurdish towns which their names ends with Diz namely RawanDiz, Qaladiz and Snandiz and Shahindiz.
The economy of Sanandaj is based upon the production of carpets, processed hides and skins, milled rice, refined sugar, woodworking, cotton weaving, metalware and cutlery.
The population of Sanandaj is mainly Kurdish. The city also had an Armenian minority who gradually immigrated from the city. Until the Iranian revolution, the city had a small Aramaic-speaking Jewish community of about 4,000 people. The city boasted a sizable Assyrian community that spoke a unique dialect of Aramaic calledSenaya; however, Senaya speakers left Sanandaj for Tehran sometime in the mid-twentieth century.