Flat Gap has an elevation of 815 feet (248 m).[2]
On June 2, 1990, one of the only tornadoes in Johnson County's history, touched down in Flat Gap at 1900. CST (7:00 p.m.) eastern time. The F1 tornado was 69 feet (23 yds) wide and created a one-mile (1.6 km) path of destruction. It caused an estimated $250,000 in damages. The only other recorded tornado happened on March 2, 2012, with widespread damage.[3]
As of the census of 2000,[4] there were 1,920 people, 732 households, and 574 families residing in the ZIP Code Tabulation Area for Flat Gap's ZIP code. The racial makeup of the ZCTA was 99.4% White, 0.2% African American, 0.2% Alaska Native/American Indian, 0.1% from other races, and 0.2% from two or more races. Hispanic or Latino of any race were 0.5% of the population.
There were 732 households, out of which 21.7% had children under the age of 18 living with them, 66.5% were married couples living together, 8.2% had a female householder with no husband present, and 21.6% were non-families. 19.7% of all households were made up of individuals, and 26.9% had someone living alone who was 65 years of age or older. The average household size was 2.62 and the average family size was 3.00.
The median income for a household was $23,409, and the median income for a family was $27,729. Males had a median income of $28,531 versus $20,179 for females. The per capita income was $13,483. About 21.9% of the families were below the poverty line.