Per the United States Census Bureau census of 2000, there were 6,149 people, 2,205 households, and 1,660 families residing in the Borough of Berlin. The population density was 663.2/km?(1,718.6/mi?. There were 2,275 housing units at an average density of 245.4/km?(635.8/mi?. The racial makeup of the borough was 94.06% White, 2.18% African American, 0.21% Native American, 1.69% Asian, 0.07% Pacific Islander, 0.49% from other races, and 1.30% from two or more races. Hispanic or Latino of any race were 2.11% of the population. 

There were 2,205 households out of which 33.6% had children under the age of 18 living with them, 60.3% were married couples living together, 11.4% had a female householder with no husband present, and 24.7% were non-families. 19.6% of all households were made up of individuals and 7.9% had someone living alone who was 65 years of age or older. The average household size was 2.76 and the average family size was 3.19. 

In the Borough of Berlin the population was spread out with 24.6% under the age of 18, 6.7% from 18 to 24, 30.3% from 25 to 44, 24.7% from 45 to 64, and 13.6% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 98.1 males. For every 100 females age 18 and over, there were 93.0 males. 

The median income for a household in the borough was $60,286, and the median income for a family was $68,704. Males had a median income of $44,211 versus $31,980 for females. The per capita income for the borough was $24,675. About 1.9% of families and 3.5% of the population were below the poverty line, including 2.7% of those under age 18 and 5.7% of those age 65 or over.