Koilwar or Koelwar (Hindi: कोइलवर) is a nagar panchayat (town) and one of the 14 community development block in Bhojpur district in the Indian state of Bihar.

Sand mining near the pillars of this old bridge has created structural problems recently.

On every 14 January and on the eve of Mahashivratri a fair takes place near the temple.

[1] The Koilwar town is very well connected by roads, highways and Rail routes to various cities like Patna, Danapur, Bihta, Arrah, Buxar, Chhapra in Bihar; and Ghazipur, Mughalsarai and Varanasi in Uttar Pradesh.

The list of 68 villages in Koilwar Block (under Arrah Tehsil) is as follows:[1] (GP is Gram Panchayat).