Mercer is the birthplace of Trent Reznor.
As of the census of 2000, there are 2,391 people, 1,020 households, and 609 families residing in the borough. The population density is 744.5/km² (1,930.3/mi²). There are 1,086 housing units at an average density of 338.2/km² (876.7/mi²). The racial makeup of the borough is 96.45% White, 2.17% African American, 0.17% Native American, 0.21% Asian, 0.04% Pacific Islander, 0.17% from other races, and 0.79% from two or more races. 0.84% of the population are Hispanic or Latino of any race.
There are 1,020 households out of which 26.8% have children under the age of 18 living with them, 43.7% are married couples living together, 13.1% have a female householder with no husband present, and 40.2% are non-families. 34.2% of all households are made up of individuals and 13.3% have someone living alone who is 65 years of age or older. The average household size is 2.24 and the average family size is 2.89.
In the borough the population is spread out with 22.2% under the age of 18, 9.2% from 18 to 24, 29.2% from 25 to 44, 22.6% from 45 to 64, and 16.8% who are 65 years of age or older. The median age is 37 years. For every 100 females there are 100.8 males. For every 100 females age 18 and over, there are 95.3 males.
The median income for a household in the borough is $29,795, and the median income for a family is $46,979. Males have a median income of $27,371 versus $19,576 for females. The per capita income for the borough is $22,161. 9.0% of the population and 6.0% of families are below the poverty line. Out of the total people living in poverty, 8.8% are under the age of 18 and 8.5% are 65 or older.