Thayer is a city located in Sangamon County Illinois. With a 2020 population of 637, it is the 788th largest city in Illinois and the 12269th largest city in the United States . Thayer is currently declining at a rate of -1.39% annually and its population has decreased by -8.08% since the most recent census, which recorded a population of 693 in 2010. Thayer reached it's highest population of in . Spanning over 1 miles, Thayer has a population density of 1,044 people per square mile.
The average household income in Thayer is $67,763 with a poverty rate of 11.75%. The median rental costs in recent years comes to $718 per month, and the median house value is $72,400. The median age in Thayer is 34.1 years, 32.7 years for males, and 34.4 years for females.