Census Data for Monmouth
Population ...
The most recent Census Estimate<1> was for 2019 and it gave Monmouth a population of 8,870 people.
The last Decennial Census<2> was in 2010, which gave Monmouth a population of 9,444 people.
The city of Monmouth is located in Warren County. The 2010 Census gave Warren County; a population of 17,707 people. This means that Monmouth had 53.3% of the county's total population, making it Warren's most populous community.
At the same time, Illinois had a population of 12,830,632 people, meaning that Monmouth had 0.07% of the total population of Illinois - making it the state's 230th most populous community.
Area ...
The 2010 Census shows that the sampling area for Monmouth has a total area of 4.23 square miles [11 km²]. Of this total, a small amount of the area is covered by water (0.02 square miles [0.1 km²]).
Warren County has a land area of 542 square miles [1,404.8 km²]. At 4.21 square miles [10.9 km²], Monmouth has 0.78% of the county's total land area.
- Continue Reading ...
- When the Census Bureau conducts a census for a city like Monmouth, they draw a boundary around the area in which they are going to conduct their count - this defines the sampling area (usually a polygon). The shape of the sampling area can be quite complex and it's important to keep in mind that the boundaries of the sampling area may or may not match the recognized boundaries of the city.
- Things like population, area and housing for Monmouth reflect the sampling area. Since the shape of the sampling area and the actual boundaries of Monmouth might be different, it's best to check with the U.S. Census Bureau to resolve any difference between the two.
- Not only does the sampling area define boundaries, it also has a GPS location (latitude & longitude) that indicates a point within the sampling area (usually the center of the polygon, known as the centroid). At the time of the 2010 Census, the sampling area was located at:
- Lat: 40° 54' 52" (or 40.91°)
- Lon: -90° 38' 29" (or -90.64°)
- More information on this topic and the changes between the 2000 Census and the 2010 Census can be found in the section for our Census-to-Census Observations ... (see below).
Housing Units ...
At the time of the 2010 Census, Monmouth had 3,792 Housing Units<3> and with its population of 9,444 people, this averages 2.49 people per Housing Unit.
- Continue Reading ...
- The 2010 Census shows Monmouth had a land area of 4.21 square miles [10.9 km²]. This translates to 896 Housing Units per square mile [346.2 housing units/km²].
- From the Census of 2000: Monmouth had 3,986 Housing Units, a population of 9,841 people and a land area of 4.03 square miles [10.4 km²]. This gives a density of 2.47 people per Housing Unit and 984 Housing Units per square mile [379.9 housing units/km²].
- Note: Repeating the caution above (under Population Density), be aware that when comparing Housing Units between the 2010 and the 2000 Census, there were changes in the sampling area for Monmouth and you need to be careful when comparing values between the censuses. More information about the changes can be found in the section called Census-to-Census Observations ... (see below).
Warren County ...
The community of Monmouth is located in Warren County<4> and is the County Seat for Warren County.
The county had a population of 17,707 people at the 2010 Census. With it's population of 9,444 people, Monmouth represented 53.3% of the county's total.
In addition, where the city of Monmouth has a population density of 2,233 people per square mile [862 people/km²], Warren County averages 32.65 people per square mile [12.6 people/km²].
For more information, please visit our Census Page for Warren County.
Census-to-Census Observations ...
Introduction ...
When the Census Bureau takes a census count (or enumeration) for Monmouth, they start by specifying the boundaries of the area to be counted. This area (or sampling area) is a polygon and its shape can be quite complex - it may or may not match the geographical boundaries of Monmouth. It's important to note that from one Census to the next, the shape and location of the polygon can change.
- Continue Reading ...
- Although we don't have specific information about the shape of the polygon for Monmouth or how it changed has over time, there is some information that can give us some hints. For example, since the shape of the sampling area is directly related to the shape of the polygon, any change to area probably indicates a new shape for the polygon.
- If you need precision or details about the methodology of the Census, you should visit the U.S. Census Bureau for a definitive answer.
Location ...
While generally coinciding with the GPS location (latitude/longitude) of Monmouth, the latitude and longitude given by the Census Bureau actually indicates the GPS location of the polygon for Monmouth.
- Continue Reading ...
- For the 2010 Census, the location was given as:
- Lat: 40.914462° (or 40°54'52" N)
- Lon: -90.641409° (or -90°38'29" W)
- For the 2000 Census, the location given was:
- Lat: 40.911531° (or 40°54'41" N)
- Lon: -90.644579° (or -90°38'40" W)
- The difference indicates that the U.S. Census Bureau moved the location of the polygon for the 2010 Census 1,380 feet to the northeast<5> of the location that was used in the 2000 Census.
- The U.S. Geological Survey (USGS) and the U.S. Board on Geographic Names (BGN) have assigned a unique GNIS identifier (#2395371) to Monmouth. This identifier also marks a GPS point on the map, and that point lies within the boundaries of Monmouth. The GNIS point has been mapped to the latitude/longitude:
- Lat: 40.914025° (or 40°54'50" N)
- Lon: -90.642010° (or -90°38'31" W)
- The GPS location given for the 2010 Census lies 229.8 feet to the northeast<6> of the point given by the GNIS for Monmouth. For more information about this and the relationship of the various Federal Codes, please visit our Misc Page for Monmouth.
Miscellaneous Information for Monmouth ...
The Federal government has assigned various identifying codes to each community, county and state. At one time or another, the US Census Bureau has used one (or more) of the following identifiers when referring to either Warren County or the city of Monmouth:
- The GNIS Codes ...
- The FIPS Codes ...
- An earlier (and largely obsolete) identification method was called the Federal Information Processing Standard (FIPS):
- State Code: 17 (Illinois)
- County Code: 187 (Warren County)
- Place Code: 50010 (Monmouth)
- State & County Code: 17/187 (Illinois / Warren County)
- State & Place Code: 17/50010 (Illinois / Monmouth)
- Misc. Census Codes ...
- Monmouth is located in Census Region #2 (the Midwest Region) and Division #3 (the East North-Central Division).
- The US Postal Service ZIP Code ...
- While some people have used a ZIP code to identify a community, the purpose of the ZIP code was to make mail delivery more efficient by grouping addresses together. Although the ZIP Code doesn't specifically identify a city like Monmouth, it does identify addresses that are in (or near) Monmouth. It's important to remember that the boundaries of a ZIP Code can be changed, re-assigned or overlapped with other ZIP Codes.
- The ZIP code for Monmouth:61462<7>
- Census ZCTA Codes ...
- The US Census Bureau created statistical entities that they call ZIP Code Tabulation Areas (ZCTAs) and these ZCTAs are frequently confused with the ZIP codes that come from the US Postal Service (USPS).
- ZCTAs were first created for the 2000 Census and at that time, they were based upon the USPS ZIP codes. While largely covering the same areas, the boundaries of a ZCTA do not necessarily match the boundaries of a postal ZIP code with the same number. For example, while a postal ZIP code can cross a county or state line, a Census ZCTA can not. They should be treated as separate entities with no correlation between them.
For more information about the various Federal identification codes, please visit our Misc Page for Monmouth.
Off-the-Road Links ...
The official website for Monmouth: www.ci.monmouth.il.us/
The official website for State of Illinois: https://illinois.gov
The official website of the U.S. Census Bureau
The official website of the U.S. Board on Geographic Names (BGN)
The official website of the U.S. Geological Survey (USGS)
Footnotes ...
| <1> | Every year, the US Census Bureau creates a population estimate for the preceeding year. Keep in mind that this value is an estimate and not an actual count. The most recent Census estimate is for the year 2019. |
| <2> | Every 10 years (eg- 1990, 2000, 2010), the US Census Bureau conducts a Constitutionally-mandated count (or enumeration) of people living within the United States. This count is called a Decennial Census. The last Decennial Census was the 2010 Census, with the next one planned for 2020. |
| <3> | A Housing Unit is a broad term for those places where people live (whether occupied or temporarily vacant), such as a house, an apartment, a mobile home, or an area that is considered as a separate living quarter. Separate living quarters (consisting of one or more rooms) are considered to be those places where people live, sleep and eat separately from others and that have access to the outside (either directly or by a shared hallway). |
| <4> | If you're interested in how the shape of Illinois' counties, including Warren, have changed over time, we recommend the Atlas of Historical County Boundaries. |
| <5> | The calculated bearing (or angle) to the 2010 Census location is 320 degrees and a distance of 1,380 feet. |
| <6> | The calculated bearing (or angle) to the GNIS point is 313 degrees and a distance of 229.8 feet. |
| <7> | When looking for a ZIP Code, whether Monmouth or elsewhere, it's always best to check the website of the United States Postal Service (USPS). |