2020 census
As of the 2020 census, there were 603 people, 231 households, and 191 families residing in the city. [6]
The median age was 38.8 years. 26.4% of residents were under the age of 18 and 16.4% of residents were 65 years of age or older. For every 100 females there were 86.7 males, and for every 100 females age 18 and over there were 82.0 males age 18 and over. [6]
0.0% of residents lived in urban areas, while 100.0% lived in rural areas. [7]
There were 231 households in Zavalla, of which 37.7% had children under the age of 18 living in them. Of all households, 38.1% were married-couple households, 18.2% were households with a male householder and no spouse or partner present, and 37.2% were households with a female householder and no spouse or partner present. About 25.1% of all households were made up of individuals and 11.7% had someone living alone who was 65 years of age or older. [6]
There were 306 housing units, of which 24.5% were vacant. The homeowner vacancy rate was 3.0% and the rental vacancy rate was 5.1%. [6]
2000 census
As of the 2000 census [3] , there were 647 people, 268 households, and 176 families residing in the city. The population density was 306.6 inhabitants per square mile (118.4/km2). There were 340 housing units at an average density of 161.1 per square mile (62.2/km2). The racial makeup of the city was 97.68% White, 0.46% Native American, 0.15% Asian, 0.62% from other races, and 1.08% from two or more races. Hispanic or Latino of any race were 2.01% of the population.
There were 268 households, out of which 34.0% had children under the age of 18 living with them, 48.1% were married couples living together, 12.7% had a female householder with no husband present, and 34.0% were non-families. 30.6% of all households were made up of individuals, and 15.3% had someone living alone who was 65 years of age or older. The average household size was 2.41 and the average family size was 2.99.
In the city, the population was spread out, with 26.6% under the age of 18, 9.0% from 18 to 24, 26.1% from 25 to 44, 24.7% from 45 to 64, and 13.6% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 87.5 males. For every 100 females age 18 and over, there were 87.7 males.
The median income for a household in the city was $21,806, and the median income for a family was $28,750. Males had a median income of $30,577 versus $20,000 for females. The per capita income for the city was $13,049. About 22.0% of families and 28.1% of the population were below the poverty line, including 36.6% of those under age 18 and 16.8% of those age 65 or over.
United States 
Texas 
