According to the United States Census Bureau, the city has a total area of 6.8 square miles (17.5 km²), of which 6.7 square miles (17.5 km²) is land; 0.04 square miles (0.1 km²) of it (0.44%) is water.
Commonwealth College was once located at the base of Rich Mountain and was known for its ties to socialism, as well as for being the one-time college of Orval Faubus, former Governor of Arkansas.
During the Clinton presidential administration, there were accusations (most notably in the controversial film Clinton Chronicles) that Clinton, during his time as governor of Arkansas, and other high-ranking state officials were involved in some way with alleged illegal cocaine importation, money laundering, and drug-use centered upon the airport in Mena. These allegations have been disputed by several different investigations, including one by the Banking Committee of the U.S. House of Representatives.
Mena was home to "Operation Black Eagle" of the Iran-Contra affair.
As of the census of 2000, there were 5,637 people, 2,431 households, and 1,546 families residing in the city. The population density was 836.4 people per square mile (322.9/km²). There were 2,771 housing units at an average density of 411.2/sq mi (158.7/km²). The racial makeup of the city was 96.91% White, 0.20% Black or African American, 0.87% Native American, 0.27% Asian, 0.05% Pacific Islander, 0.50% from other races, and 1.21% from two or more races. About 2.18% of the population were Hispanic or Latino of any race.
There were 2,431 households, out of which 27.5% had children under the age of 18 living with them, 49.7% were married couples living together, 10.9% had a female householder with no husband present, and 36.4% were non-families. 33.7% of all households were made up of individuals, and 18.9% had someone living alone who was 65 years of age or older. The average household size was 2.24, and the average family size was 2.85.
In the city, the population was spread out, with 23.1% under the age of 18, 7.7% from 18 to 24, 23.8% from 25 to 44, 20.9% from 45 to 64, and 24.5% who were 65 years of age or older. The median age was 41 years. For every 100 females, there were 84.1 males. For every 100 females, age 18 and over, there were 79.9 males.
The median income for a household in the city was $22,671, and the median income for a family was $30,164. Males had a median income of $23,665 versus $18,472 for females. The per capita income for the city was $14,710. About 12.1% of families and 17.6% of the population were below the poverty line, including 22.8% of those under age 18 and 16.8% of those age 65 or over.
The city is served by Mena Intermountain Municipal Airport.