The first settlers, Sidney Evans and P.G. Harrington, arrived in the northeastern part of  what is now the City of New Berlin in 1836. The area first came under local government in 1838 as part of the Town of Muskego, which at the time, was composed of New Berlin and Muskego. The area that is now the City of New Berlin was separated from the Town of  Muskego in 1839 and given the name, Town of Mentor.

On January 13, 1840, the Town of Mentor became the Town of New Berlin. It was named by Sidney Evans in honor of his hometown, New Berlin, New York.   The town remained a rural and agricultural area until the 1940s when the westward migration to the suburbs from Milwaukee began. Between 1850 and 1950, New Berlin's population went from 1,293 to 5,334.  Ten years later, in 1960, the population had nearly tripled to 15,788. The Town of New Berlin became the City of New Berlin with its incorporation in 1959.