Nitro is a city in Kanawha and Putnam counties in the U.S. state of West Virginia. It takes its name from a World War I era nitrocellulose plant. …Nitro is a city in Kanawha and Putnam counties in the U.S. state of West Virginia. It takes its name from a World War I era nitrocellulose plant. The population was 6,618 according to the 2020 census. It is part of the Charleston metropolitan area.