New Berlin is a city in eastern Waukesha County, Wisconsin, United States. The population was 40,451 at the 2020 census. It is part of th…New Berlin is a city in eastern Waukesha County, Wisconsin, United States. The population was 40,451 at the 2020 census. It is part of the Milwaukee metropolitan area. Area residents put the accent on the first syllable of Berlin, rather than the second.