Earlier in the borough's history, manufacturers made tons of enameled porcelain ware, glass, tile, tubing, drawn steel and wire. Thiel College was founded here in 1866 and moved to Greenville five years later.
In 1900, the population was 2,008; in 1910, 3,376; and in 1940, 7,061 people were residents.
In early November 2003, the largest hepatitis A outbreak in American history occurred due to contaminated green onions at the defunct Chi-Chi's Mexican restaurant in the Beaver Valley Mall in Monaca. There were at least 660 confirmed cases, and four deaths.
As of the census of 2000, there were 6,286 people, 2,709 households, and 1,741 families residing in the borough. The population density was 3,004.0 people per square mile (1,161.3/km²). There were 2,892 housing units at an average density of 1,382.1/sq mi (534.3/km²). The racial makeup of the borough was 97.1% White, 1.9% African American, 0.2% Asian, 0% from other races, and 0.7% from two or more races. Hispanic or Latino of any race were 0.6% of the population.
There were 2,709 households out of which 26.8% had children under the age of 18 living with them, 47.6% were married couples living together, 12.7% had a female householder with no husband present, and 35.7% were non-families. 32.2% of all households were made up of individuals and 18.8% had someone living alone who was 65 years of age or older. The average household size was 2.31 and the average family size was 2.93.
In the borough the population was spread out with 22.0% under the age of 18, 6.8% from 18 to 24, 26.9% from 25 to 44, 23.2% from 45 to 64, and 21.1% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 87.3 males. For every 100 females age 18 and over, there were 83.4 males.
The median income for a household in the borough was $33,706, and the median income for a family was $45,046. Males had a median income of $35,436 versus $24,375 for females. The per capita income for the borough was $17,001. About 8.1% of families and 8.9% of the population were below the poverty line, including 16.7% of those under age 18 and 3.1% of those age 65 or over.