At the time of the 2006 National Census, the village's population was 839 in 179 households, when it was in Sabalan Rural District of the former Sareyn District of Ardabil County. The following census in 2011 counted 979 people in 264 households, by which time the district had been separated from the county in the establishment of Sareyn County. The rural district was transferred to the new Sabalan District, and Sain was transferred to Arjestan Rural District created in the district. The 2016 census measured the population of the village as 947 people in 276 households. It was the most populous village in its rural district.
^Sa'in can be found at GEOnet Names Server, at this link, by opening the Advanced Search box, entering "-3771221" in the "Unique Feature Id" form, and clicking on "Search Database".
^Davodi, Parviz (15 July 2009) [Approved 24 April 1388]. "With the approval of the government, Sareyn became a county". irna.ir (in Persian). Ministry of the Interior, Political and Defense Commission of the Government. Archived from the original on 5 November 2023. Retrieved 5 November 2023 – via Islamic Republic News Agency.
