Keystone is a city located in South Dakota. With a 2020 population of 339, it is the 149th largest city in South Dakota and the 14880th largest city in the United States. Keystone is currently declining at a rate of -0.29% annually but its population has increased by 0.59% since the most recent census, which recorded a population of 337 in 2010. Keystone reached it's highest population of 341 in 2013. Spanning over 3 miles, Keystone has a population density of 119 people per square mile.
The average household income in Keystone is $57,175 with a poverty rate of 19.09%. The median rental costs in recent years comes to $442 per month, and the median house value is $124,100. The median age in Keystone is 32.4 years, 25.8 years for males, and 39.2 years for females. For every 100 females there are 118.6 males.