Nilsiä is a former small town and a municipality of Finland.
It is located in the province of Eastern Finland and is part of the Northern Savonia region. The town has a population of 6,528 (31 December 2012) and covers an area of 847.71 square kilometres (327.30sqmi) of which 136.14km (52.56sqmi) is water. The population density is 9.1741/km (23.7608/sqmi).