Cook County Housing Age: Year Built By Township, 2025

Just over half of the houses and small apartment buildings in the Cook County Assessor’s 2025 records — 50.1 percent — were built in 1954 or earlier, and 24,481 of the 1.1 million — 2.2 percent — were built in 2010 or later. In the assessor’s eight Chicago townships the middle year is 1925 — at least half their buildings date from then or earlier — against 1960 in the county’s 30 suburban townships.

Single and Multi-Family Improvement Characteristics (x54s-btds), maintained by the Cook County Assessor’s Office, tax-year 2025 rows, retrieved September 18, 2026; last updated September 15, 2026 · one row per building: single-family houses and buildings of fewer than seven units, not condominiums · township names from the assessor’s Parcel Universe (pabr-t5kh) · counts by year built are buildings still in the 2025 rows, not how many went up in each decade

Which decade left the most of what still stands?

The file covers single-family houses and buildings of up to six units. Buildings by the year it records them as built, among the 1,103,031 with a recorded year; 16 have none. A decade’s count is what was still standing, and still in this file, in 2025.
Decade built	Buildings in the 2025 rows	Share
Before 1900	81,608	7.4%
1900s	55,071	5.0%
1910s	72,651	6.6%
1920s	126,523	11.5%
1930s	24,156	2.2%
1940s	78,970	7.2%
1950s	246,168	22.3%
1960s	155,663	14.1%
1970s	91,070	8.3%
1980s	47,763	4.3%
1990s	52,448	4.8%
2000s	46,459	4.2%
2010s	15,268	1.4%
2020 to 2025	9,213	0.8%

The 1950s, with 246,168 buildings, 22.3 percent. That is more than the 1900s and 1910s together (127,722) and about three and a half times everything dated 2000 or later (70,940). The 1930s, the Depression decade, left 24,156, fewer than a fifth of the 1920s’ 126,523. Read the table as survival as much as construction: every building torn down since is missing from its decade, and the older a decade, the longer its buildings have had to disappear.

Chicago’s townships against the suburbs

Middle year: the year by which at least half of the buildings with a recorded year had been built. Chicago’s eight townships are the ones the assessor groups as its City triad, one of the three groups it reassesses in turn.
Area	Buildings	Middle year built	Built before 1940	Built 2010 or later
Chicago’s eight townships	439,409	1925	58.6%	8,935 (2.0%)
The 30 suburban townships	663,622	1960	15.4%	15,546 (2.3%)
All of Cook County	1,103,031	1954	32.6%	24,481 (2.2%)

In Chicago’s townships 58.6 percent of these buildings date from before 1940; in the suburban townships, 15.4 percent. Since 2010 the two sit close together: 2.0 percent of the city townships’ buildings and 2.3 percent of the suburban ones. By this measure the gap in age was set generations ago, and the recent pace of new building, relative to what stands, is about even.

Township by township

Oldest middle year first. These are the assessor’s township lines, not city or village limits; a suburban township can be larger than the town that shares its name.
Township	Group	Buildings	Middle year built	Built before 1940	Built 2010 or later
South Chicago	Chicago	16,487	1903	58.4%	1,231 (7.5%)
West Chicago	Chicago	65,664	1906	83.0%	2,180 (3.3%)
Lake View	Chicago	23,046	1908	70.9%	1,800 (7.8%)
Oak Park	Suburban	11,448	1916	87.3%	141 (1.2%)
North Chicago	Chicago	5,481	1920	53.4%	402 (7.3%)
Cicero	Suburban	13,767	1922	71.4%	29 (0.2%)
Berwyn	Suburban	12,994	1925	71.6%	62 (0.5%)
Hyde Park	Chicago	64,699	1926	55.4%	808 (1.2%)
Evanston	Suburban	13,171	1927	57.7%	251 (1.9%)
Jefferson	Chicago	112,919	1927	60.3%	1,821 (1.6%)
River Forest	Suburban	2,977	1927	62.2%	73 (2.5%)
Rogers Park	Chicago	7,814	1938	50.5%	73 (0.9%)
Lake	Chicago	143,299	1944	46.3%	620 (0.4%)
Riverside	Suburban	5,262	1947	39.1%	40 (0.8%)
Leyden	Suburban	23,297	1952	18.3%	156 (0.7%)
Proviso	Suburban	41,984	1952	30.2%	245 (0.6%)
Calumet	Suburban	4,730	1953	35.3%	2 (0.0%)
New Trier	Suburban	18,330	1954	36.6%	1,188 (6.5%)
Niles	Suburban	31,794	1956	4.5%	518 (1.6%)
Norwood Park	Suburban	8,214	1957	9.9%	143 (1.7%)
Thornton	Suburban	53,478	1957	17.1%	44 (0.1%)
Lyons	Suburban	30,466	1958	19.4%	1,491 (4.9%)
Maine	Suburban	35,463	1958	10.6%	1,142 (3.2%)
Stickney	Suburban	12,293	1958	5.0%	212 (1.7%)
Worth	Suburban	43,461	1958	8.5%	329 (0.8%)
Bloom	Suburban	27,442	1961	13.9%	305 (1.1%)
Elk Grove	Suburban	17,980	1963	1.8%	156 (0.9%)
Wheeling	Suburban	36,373	1965	3.3%	956 (2.6%)
Bremen	Suburban	32,865	1966	6.1%	463 (1.4%)
Northfield	Suburban	23,927	1970	2.9%	1,942 (8.1%)
Palatine	Suburban	27,519	1972	2.1%	1,066 (3.9%)
Palos	Suburban	14,003	1972	2.0%	305 (2.2%)
Rich	Suburban	22,475	1972	2.1%	307 (1.4%)
Schaumburg	Suburban	30,491	1973	0.1%	512 (1.7%)
Barrington	Suburban	5,577	1984	9.6%	543 (9.7%)
Hanover	Suburban	25,178	1985	1.3%	576 (2.3%)
Orland	Suburban	28,507	1987	0.5%	993 (3.5%)
Lemont	Suburban	8,156	1995	8.3%	1,356 (16.6%)

South Chicago township’s middle year is 1903, West Chicago’s 1906 and Lake View’s 1908; Oak Park, at 1916, is the oldest suburban township. At the other end, Lemont’s middle year is 1995, Orland’s 1987 and Hanover’s 1985. Old and new are not opposites here. Lake View (7.8 percent), South Chicago (7.5) and North Chicago (7.3) carry three of the six highest shares of buildings dated 2010 or later, and West Chicago holds the most of them in number, 2,180. Lake, the county’s largest township by this count with 143,299 buildings, has 620 — 0.4 percent. Lemont leads on share, with 1,356 buildings, 16.6 percent of its own.

Is Cook County adding to this stock?

Every row the file holds for each tax year, including the 16 in 2025 with no recorded year built. The 2026 rows are not final.
Tax year	Buildings in the file
1999	1,059,702
2000	1,077,974
2001	1,078,951
2002	1,081,904
2003	1,085,834
2004	1,089,762
2005	1,093,404
2006	1,096,341
2007	1,098,544
2008	1,099,960
2009	1,099,466
2010	1,099,597
2011	1,099,010
2012	1,098,752
2013	1,098,025
2014	1,097,705
2015	1,098,115
2016	1,098,108
2017	1,098,637
2018	1,098,786
2019	1,098,966
2020	1,099,085
2021	1,099,631
2022	1,100,289
2023	1,101,227
2024	1,102,672
2025	1,103,047

Barely, by this file’s count. It grew every year from 2000 through 2008, by 21,986 buildings in all, then all but stopped: the 2025 count, 1,103,047, is the file’s highest, but only 3,087 above 2008’s, after a low of 1,097,705 in 2014. (1999, the file’s first year, holds 18,272 fewer rows than 2000, so this page measures growth from 2000.) The 2026 rows, which the file says are final only once the assessor certifies every township, hold 1,102,622 so far.

Set that beside the 24,481 buildings dated 2010 or later, and our arithmetic suggests the stock turned over more than it grew. If year built marks when a building went up — the field is labeled simply “Year built” — and the file counted buildings the same way in both years, then roughly 21,394 or more buildings in the 2008 rows are no longer in the 2025 rows: torn down, converted to condominiums, moved to another property class or otherwise dropped. That is our estimate from grouped counts, not a figure the file records, and corrections to year-built values or classes since 2008 would move it.

What the file confirms, and what it cannot tell you

Confirmed, as recorded: how many buildings the assessor lists by tax year, township and year built. Not shown: condominiums, which the file does not carry, and buildings of seven or more units; which buildings left and why; and anything about owners or occupants. This page read only grouped counts, never a parcel number or an address. The year-built field bunches at some round years — 8,011 buildings are dated 1910, against 3,807 in 1909 and 5,158 in 1911 — which we read as estimated dates for some older buildings, so decades are steadier than single years. Rows are buildings, not parcels: 15,281 sit on parcels with more than one building.

Where the record lives

The Single and Multi-Family Improvement Characteristics file and the current-year Parcel Universe, which supplied the township names, sit on Cook County’s data portal. Every figure here was computed from them as retrieved on September 18, 2026.

The bottom line

Cook County’s houses and small apartment buildings are mostly mid-century and older: just over half date from 1954 or earlier, and the 1950s left more of them than any other decade. Their count has barely moved since 2008, and 2.2 percent date from 2010 or later.

Three questions the file can answer

Which township’s middle year is the oldest? South Chicago’s, 1903. The newest? Lemont’s, 1995. Which decade left the most buildings still in the 2025 rows? The 1950s, with 246,168.

Source: the Cook County Assessor’s Single and Multi-Family Improvement Characteristics file (x54s-btds), tax-year 2025 rows and each year’s row count, retrieved September 18, 2026.
Read: grouped counts by tax year, township and year built; no parcel number, address or owner field selected.
Townships: codes matched to names in the assessor’s current-year Parcel Universe (pabr-t5kh); the eight in its City triad are reported as Chicago’s.
Middle year: counting from the oldest, the year by which at least half of the buildings with a recorded year had been built.
Not here: condominiums, larger apartment buildings, and any cause for the patterns.

Computed by KCM Desk from the Cook County Assessor’s Single and Multi-Family Improvement Characteristics file, retrieved September 18, 2026. Human-guided and edited — about this desk. If you spot an error, corrections come first.