Originally the settlement was called White Plains, but when the city was incorporated in 1874, the name was changed. It was decided that Kings Mountain would be a more appropriate name since the community was the closest town to the historic Battle of Kings Mountain.
There were 3,821 households out of which 30.7% had children under the age of 18 living with them, 49.4% were married couples living together, 17.2% had a female householder with no husband present, and 30.0% were non-families. 26.8% of all households were made up of individuals and 12.6% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 2.98.
In the city the population was spread out with 25.3% under the age of 18, 7.4% from 18 to 24, 27.3% from 25 to 44, 22.4% from 45 to 64, and 17.6% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 85.9 males. For every 100 females age 18 and over, there were 80.4 males.
The median income for a household in the city was $31,415, and the median income for a family was $39,137. Males had a median income of $32,444 versus $22,201 for females. The per capita income for the city was $15,920. About 13.4% of families and 19.2% of the population were below the poverty line, including 29.2% of those under age 18 and 20.7% of those age 65 or over.
The city is home to Parker Hannifin's Gear Pump Division.