Harnathpur is a village in Raghunathpur tehsil in district of Siwan, Bihar, India. As per the data provided by Census of India in 2011, total population of Harnathpur was 4,536 which includes 2,243 males and 2,293 females. Harnathpur covers 417 ha area. Pincode of Harnathpur is N/A.