The total area of the block is 69.17 square kilometres (26.71 sq mi) and the total population of the block is 113,499.

[1] Mairwa city is the headquarters of this block.

[2] Some villages of Mairwa block in different panchayats are: Mairwa, situated in the western part of Bihar, borders the Indian state of Uttar Pradesh.

It was originally a block of Siwan district, approximately 20 km from Siwan which in ancient days formed a part of Kosala Kingdom.

Mairwa is bounded on the east by the Siwan district headquarters, on the north by Gopalganj district and on the west and south by two districts of Uttar Pradesh: Deoria and Ballia.