Cassoday is a city in Butler County, Kansas, United States. It is known as the "Prairie Chicken Capital of the World." As of the 2010 census, the city population was 129.
Cassoday is located at 38°2′19″N 96°38′18″W / 38.03861°N 96.63833°W / 38.03861; -96.63833 (38.038545, -96.638252), in the scenic Flint Hills. According to the United States Census Bureau, the city has a total area of 0.3 square miles (0.9 km²), all of it land.
As of the census of 2000, there were 130 people, 54 households, and 36 families residing in the city. The population density was 393.4 people per square mile (152.1/km²). There were 57 housing units at an average density of 172.5 per square mile (66.7/km²). The racial makeup of the city was 100.00% White. Hispanic or Latino of any race were 3.85% of the population.