Eureka is a city located in South Dakota. With a 2020 population of 828, it is the 74th largest city in South Dakota and the 11137th largest city in the United States. Eureka is currently declining at a rate of -0.36% annually and its population has decreased by -4.61% since the most recent census, which recorded a population of 868 in 2010. Eureka reached it's highest population of 864 in 2010. Spanning over 1 miles, Eureka has a population density of 888 people per square mile.
The average household income in Eureka is $48,083 with a poverty rate of 14.30%. The median rental costs in recent years comes to $540 per month, and the median house value is $50,400. The median age in Eureka is 59.7 years, 52.1 years for males, and 65.6 years for females. For every 100 females there are 82.0 males.