Illinois

Mercer

15,699
2020 population
1830
first census record
20
census records

About Mercer

Mercer, Illinois, first appears in the United States federal census in 1830, when it recorded a population of 26. At the most recent census, in 2020, its population stood at 15,699.

Its recorded population peaked at 20,945 in 1900, and has since declined by roughly 25 percent.

On the ground today, 12 places are listed on the National Register of Historic Places.

Population by decade

Census YearPopulationChart
202015,699
201016,434
200016,957
199017,290
198019,286
197017,294
196017,149
195017,374
194017,701
193016,641
192018,800
191019,723
190020,945
189018,545
188019,502
187018,769
186015,042
18505,246
18402,352
183026
Source

Population data from the United States decennial census, U.S. Census Bureau (public domain).

Historic places in Mercer

National Register of Historic Places listings in Mercer, Illinois.

Mercer County Jail
Aledo
Commercial House
Keithsburg
Willits, Levi, House
New Boston
Mercer County Courthouse
Aledo
Lock and Dam No. 17 Historic District
New Boston
Mercer County Fairgrounds
Aledo
Downtown Aledo Historic District
Aledo
Keithsburg Historic District
Keithsburg
Sherrard Banking Company
Sherrard
Ives, Gideon, House
New Boston
Thompson, James S., House
New Boston
Browse all Illinoishistoric sites ›

Other counties in Illinois

Explore census history and historic records for more Illinois counties.

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Everything a full report reveals about Mercer County, Illinois

This page charts the census history of Mercer County, Illinois. A full Aubrey report for an address here pulls together everything the historical record holds about the ground, from the earliest settlement to the twentieth century:

Overview
An interactive map of the location with historic sites, battles and Native heritage plotted, and its full story era by era.
The Land
The historic sites and place names around the location, and how this land was settled and used.
Geology
The bedrock beneath the site, its age and rock type, reaching back millions of years.
LiDAR Terrain
Laser-scanned terrain that reveals earthworks and old features hidden in the landscape.
Conflict & War
The battles, raids and skirmishes fought near here, across every era of American conflict.
The Civil War
The Civil War on this ground, 1861 to 1865: who held it, and the battles, camps and regiments nearby.
The Soldiers
The men who marched from here in the Civil War, named and traced where the record allows.
Native Heritage
The Native nations who held this land, mapped across time from before European contact to today.
Settlement
Who claimed and held this ground, from Indigenous homelands through the colonial powers to the United States.
The Community
How the town grew, who came, and what kind of place it became, traced through the census record.
Rivers & Rail
The rivers, canals and railroads that connected this place between 1830 and 1911.
Notable People
The people born, buried or genuinely tied to this exact place, with their stories.
Historical Maps
Historic maps of the location layered over how it looks today.
Finds & Access
Museum objects tied to the area, and the laws on searching, collecting and access here.
Literature
The old books, county histories and archives that mention this place, quoted with their sources.
Spotlight
A deep dive into the most remarkable, lesser-known history of the place, traced back to the record.
Points of Interest
The most significant historic sites and landmarks near the location, and why they matter.
Timeline
The whole story of the location told era by era, from first peoples to the present day.
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Illinoishistory ›NRHP historic sites ›Notable people from Illinois›

Frequently asked about Mercer

When does Mercer first appear in the US census?
Mercer, Illinois first appears in the federal census in 1830, with a recorded population of 26.
What is the population of Mercer?
At the most recent federal census (2020), Mercer had a recorded population of 15,699.
When did Mercer's population peak?
Mercer's recorded population peaked at 20,945 in 1900.
How many historic places are in Mercer?
12 sites are listed on the National Register of Historic Places in Mercer, Illinois.
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