In 1912, Arma was said to be "an incorporated town of Crawford county, is a station on the Missouri Pacific R. R., 9 miles east of Girard, the county seat, and about 3 miles west of the state line. It is a typical Kansas town, has express and telegraph offices, a flour mill, a lumber yard, several general stores, and in 1910 reported a population of 327."
From Frank W. Blackmar's History of Kansas (1912)
Arma is located at 37°32'37N, 94°42'2W (37.543679, -94.700472). According to the United States Census Bureau, the city has a total area of 2.7 km² (1.0 mi²). 2.7 km² (1.0 mi²) of it is land and 0.95% is water.
As of the census of 2000, there were 1,529 people, 669 households, and 398 families residing in the city. The population density was 567.6/km² (1,467.5/mi²). There were 735 housing units at an average density of 272.9/km² (705.4/mi²). The racial makeup of the city was 97.84% White, 0.46% African American, 0.46% Native American, 0.13% Asian, 0.07% Pacific Islander, 0.07% from other races, and 0.98% from two or more races. Hispanic or Latino of any race were 0.92% of the population.
There were 669 households out of which 26.8% had children under the age of 18 living with them, 49.0% were married couples living together, 6.7% had a female householder with no husband present, and 40.4% were non-families. 37.1% of all households were made up of individuals and 19.7% had someone living alone who was 65 years of age or older. The average household size was 2.20 and the average family size was 2.91.
In the city the population was spread out with 21.4% under the age of 18, 7.9% from 18 to 24, 25.2% from 25 to 44, 22.4% from 45 to 64, and 23.1% who were 65 years of age or older. The median age was 42 years. For every 100 females there were 88.3 males. For every 100 females age 18 and over, there were 87.8 males.
The median income for a household in the city was $26,658, and the median income for a family was $36,648. Males had a median income of $27,337 versus $19,821 for females. The per capita income for the city was $15,636. About 8.4% of families and 11.9% of the population were below the poverty line, including 14.4% of those under age 18 and 15.8% of those age 65 or over.