The history of Niemirow probably dates back to the 11th century, when a Slavic gord existed here. Archaeological findings proved that both Mazovian and Ruthenian settlers resided here. First documented mention of the village comes from 1495; at that time, it was called Niwice. In 1548, King Zygmunt August handed the village to a nobleman Stanislaw Niemira (Gozdawa coat of arms), whose grandson, Castellan of Podlasie Stanislaw Niemira, changed the name of the village into Niemirow and granted town charter to it. In 1620, a market square with a parish church were built, and Niemirow was first called a town in documents from 1631. Swedish and Transilvanian invasion of Poland (1655–1660) had catastrophic consequences for the town, as it was completely destroyed, and in 1662 its population was only 88.