Mangatainoka is a small settlement in the Tararua District of New Zealand's North Island. It is located on the banks of the Mangatainoka River, 5 km (3.1 mi) north of Pahiatua. The 2001 New Zealand Census of Population and Dwellings gave its population as 1,617, consisting of 858 males and 759 females, representing a decline of 7.4% or 129 people since the 1996 census.