Census Data for Alton
Population ...
The most recent Census Estimate<1> was for 2019 and it gave Alton a population of 26,262 people.
The last Decennial Census<2> was in 2010, which gave Alton a population of 27,865 people.
The city of Alton is located in Madison County. The 2010 Census gave Madison County; a population of 269,282 people. This means that Alton had 10.35% of the county's total population, making it Madison's 2nd most populous community.
At the same time, Illinois had a population of 12,830,632 people, meaning that Alton had 0.22% of the total population of Illinois - making it the state's 76th most populous community.
Area ...
The 2010 Census shows that the sampling area for Alton has a total area of 16.74 square miles [43.3 km²]. Of this total, 15.47 square miles [40.1 km²] is land, with the balance (7.56%) being water (1.27 square miles [3.3 km²]).
Madison County has a land area of 715 square miles [1,853.3 km²]. At 15.47 square miles [40.1 km²], Alton has 2.16% of the county's total land area.
- Continue Reading ...
- When the Census Bureau conducts a census for a city like Alton, 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 Alton reflect the sampling area. Since the shape of the sampling area and the actual boundaries of Alton 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: 38° 54' 7" (or 38.9°)
- Lon: -90° 9' 14" (or -90.15°)
- 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, Alton had 13,266 Housing Units<3> and with its population of 27,865 people, this averages 2.1 people per Housing Unit.
- Continue Reading ...
- The 2010 Census shows Alton had a land area of 15.47 square miles [40.1 km²]. This translates to 792 Housing Units per square mile [306 housing units/km²].
- From the Census of 2000: Alton had 13,894 Housing Units, a population of 30,496 people and a land area of 15.64 square miles [40.5 km²]. This gives a density of 2.19 people per Housing Unit and 836 Housing Units per square mile [323.1 housing units/km²].
- Note: Repeating the caution above (under Population Density), be aware that when comparing Housing Units between the 2010 Census and the 2000 Census, there were changes in the sampling area for Alton and you need to be careful when comparing numbers between the censuses. More information about the changes can be found in the section called Census-to-Census Observations ... (see below).
Madison County ...
Alton is located in Madison County<4>.
The county had a population of 269,282 people at the 2010 Census. With it's population of 27,865 people, Alton represented 10.35% of the county's total.
In addition, where the city of Alton has a population density of 1,664 people per square mile [642 people/km²], Madison County averages 376.3 people per square mile [145.3 people/km²].
For more information, please visit our Census Page for Madison County.
Census-to-Census Observations ...
Introduction ...
When the Census Bureau takes a census count (or enumeration) for Alton, 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 Alton. 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 Alton 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 Alton, the latitude and longitude given by the Census Bureau actually indicates the GPS location of the polygon for Alton.
- Continue Reading ...
- For the 2010 Census, the location was given as:
- Lat: 38.902125° (or 38°54'7" N)
- Lon: -90.154083° (or -90°9'14" W)
- For the 2000 Census, the location given was:
- Lat: 38.900438° (or 38°54'1" N)
- Lon: -90.159844° (or -90°9'35" W)
- The difference indicates that the U.S. Census Bureau moved the location of the polygon for the 2010 Census 1,746 feet to the east<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 (#2393935) to Alton. This identifier also marks a GPS point on the map, and that point lies within the boundaries of Alton. The GNIS point has been mapped to the latitude/longitude:
- Lat: 38.903294° (or 38°54'11" N)
- Lon: -90.152330° (or -90°9'8" W)
- The GPS location given for the 2010 Census lies 654 feet to the southwest<6> of the point given by the GNIS for Alton. For more information about this and the relationship of the various Federal Codes, please visit our Misc Page for Alton.
Miscellaneous Information for Alton ...
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 Madison County or the city of Alton:
- 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: 119 (Madison County)
- Place Code: 01114 (Alton)
- State & County Code: 17/119 (Illinois / Madison County)
- State & Place Code: 17/01114 (Illinois / Alton)
- Misc. Census Codes ...
- Alton 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 Alton, it does identify addresses that are in (or near) Alton. 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 Alton:62002<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 Alton.
Off-the-Road Links ...
The official website for Alton: www.alton-il.com/
The official website for Madison County: www.co.madison.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 Madison, have changed over time, we recommend the Atlas of Historical County Boundaries. |
| <5> | The calculated bearing (or angle) to the 2010 Census location is 290 degrees and a distance of 1,746 feet. |
| <6> | The calculated bearing (or angle) to the GNIS point is 130 degrees and a distance of 654 feet. |
| <7> | When looking for a ZIP Code, whether Alton or elsewhere, it's always best to check the website of the United States Postal Service (USPS). |