Allardt is a city in Fentress County, Tennessee, United States. The population was 642 at the 2000 census.
According to the United States Census Bureau, the city has a total area of 3.8 square miles (9.8 km²), all of it land.
As of the census of 2000, there were 642 people, 259 households, and 197 families residing in the city. The population density was 170.0 people per square mile (65.6/km²). There were 283 housing units at an average density of 74.9 per square mile (28.9/km²). The racial makeup of the city was 98.91% White, 0.16% Native American, 0.16% Asian, and 0.78% from two or more races. Hispanic or Latino of any race were 0.31% of the population.