Siwan is a city and nagar parishad in the Indian state of Bihar. It is the administrative headquarters of Siwan district and one of the urban settlements out of three in the district. It is located close to Uttar Pradesh.
Siwan, situated in the western part of the State, was originally a sub-division of Saran District, which in ancient days formed a part of Kosala Kingdom. The present district limits came into existence only in 1972, which is geographically situated at 25.58 to 26.23 North and 84.10 to 84.47 east. The total area of the Siwan district is about 2219.00 Sq. Km. with a population of 33,30,464 as per the 2011 census. The district is bounded on the east by the Saran district, on the north by Gopalganj district and on the west and south by two districts of U.P. viz. Deoria and Balia respectively.