Iowa

O'Brien

14,182
2020 population
1860
first census record
17
census records

About O'Brien

O'Brien, Iowa, first appears in the United States federal census in 1860, when it recorded a population of 8. At the most recent census, in 2020, its population stood at 14,182.

Its recorded population peaked at 19,293 in 1940, and has since declined by roughly 26 percent.

Population by decade

Census YearPopulationChart
202014,182
201014,398
200015,102
199015,444
198016,972
197017,522
196018,840
195018,970
194019,293
193018,409
192019,051
191017,262
190016,985
189013,060
18804,155
1870715
18608
Source

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

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Everything a full report reveals about O'Brien County, Iowa

This page charts the census history of O'Brien County, Iowa. 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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Frequently asked about O'Brien

When does O'Brien first appear in the US census?
O'Brien, Iowa first appears in the federal census in 1860, with a recorded population of 8.
What is the population of O'Brien?
At the most recent federal census (2020), O'Brien had a recorded population of 14,182.
When did O'Brien's population peak?
O'Brien's recorded population peaked at 19,293 in 1940.
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