Monmouth is a city located in Warren County Illinois. Monmouth has a 2020 population of 9,724. It is also the county seat of Warren County. Monmouth is currently declining at a rate of -0.87% annually and its population has decreased by -7.10% since the most recent census, which recorded a population of 10,467 in 2010. Monmouth reached it's highest population of 10,564 in 2011.
The average household income in Monmouth is $57,025 with a poverty rate of 16.12%. The median rental costs in recent years comes to $621 per month, and the median house value is $79,900. The median age in Monmouth is 36.2 years, 35.7 years for males, and 36.6 years for females.