Population and median age, 1820–2024
Median age is the age that splits a population in half. In 1820 half of all Americans were younger than 17: a country of children, with large families on cheap land. By 2024 the median was 39. Two things push it up: fewer births per woman, and longer lives. One thing pulled it down for a while: the baby boom of 1946–64, visible as the dip from 30.2 in 1950 to 28.1 in 1970.
What median age signals: a young median means many dependents per worker, cheap labor ahead, and demand for schools. An old median means more retirees per worker, pressure on pensions and health care, and, for cities, demand for smaller homes, elevators and transit. The towers that rise downtown after 2000 are partly a median-age story: older and childless households choose apartments.
Lessons: E22.1 The pyramidPreview E22.3 Why do birth rates fall?Preview E22.4 The momentum effectPreview
Drawer: People, Ages and Arrivals: Births or Boats?
Supplement: U.S. Census Bureau: population estimates
Births or boats? When immigration drove growth
A population grows two ways: natural increase (births minus deaths) and net migration (arrivals minus departures). For most of American history natural increase did most of the work. The table divides each decade's recorded arrivals by that decade's growth. It is an upper bound: many arrivals went home again (perhaps a third of Italians and Greeks before 1914), so the net share was lower.
| Decade | Growth (M) | Arrivals (M) | Arrivals ÷ growth |
|---|---|---|---|
| 1820s | 3.23 | 0.13 | 4% |
| 1830s | 4.20 | 0.54 | 13% |
| 1840s | 6.12 | 1.43 | 23% |
| 1850s | 8.25 | 2.81 | 34% |
| 1860s | 7.12 | 2.08 | 29% |
| 1870s | 11.63 | 2.74 | 24% |
| 1880s | 12.79 | 5.25 | 41% |
| 1890s | 13.23 | 3.69 | 28% |
| 1900s | 16.02 | 8.20 | 51% |
| 1910s | 13.79 | 6.35 | 46% |
| 1920s | 17.18 | 4.30 | 25% |
| 1930s | 8.96 | 0.70 | 8% |
| 1940s | 19.17 | 0.86 | 4% |
| 1950s | 27.99 | 2.50 | 9% |
| 1960s | 23.89 | 3.21 | 13% |
| 1970s | 23.34 | 4.25 | 18% |
| 1980s | 22.16 | 6.24 | 28% |
| 1990s | 32.71 | 9.78 | 30% |
| 2000s | 27.33 | 10.30 | 38% |
| 2010s | 22.70 | 10.55 | 46% |
The peaks. The 1880s and the 1900s are the classic immigration decades: arrivals equal to roughly 40–50% of growth. The 1930s are the opposite: Depression and the 1924 quota law cut arrivals to almost nothing. The 1990s–2010s rise again to a third or more of growth as births fall.
The new turn. Since 2021 the Census Bureau's annual estimates show net international migration larger than natural increase, the first sustained stretch of that kind in the modern series. Births barely outnumber deaths in an aging country, so migration now decides whether the nation grows at all.
| Year | Natural increase | Net migration | Estimate |
|---|---|---|---|
| 2021 | 148k | 376k | Vintage 2021 |
| 2022 | 245k | 1,010k | Vintage 2022 |
| 2024 | 519k | 2,786k | Vintage 2024 |
Vintages are revised; later releases change earlier years (2024 used a new migration method).
Lessons: E22.2 The transition's stagesPreview E22.5 The projection testPreview APHG 2 The transition machinePreview
Supplement: U.S. Census Bureau: components of population change
Arrivals by decade and the foreign-born share
Bars show people granted permanent residence each decade. The line shows the share of residents born abroad. Notice the gap: the share peaked near 15% in 1890 and 1910, fell to 4.7% by 1970 after four decades of restriction, and has climbed back to about 14% today, close to the old record.
Where they came from: eight marquee years
Each pie shows the origins of that year's arrivals. Read them left to right as a relay: Ireland and Britain hand off to Germany, then to southern and eastern Europe, then, after the 1965 Hart-Celler Act ended national-origin quotas, to Latin America and Asia. The 2025 pie uses the latest published yearbook (FY2023).
1820
1870
1890
1910
1950
1975
1995
2025
Approx.: shares are rounded from DHS Yearbook Table 2 (country or region of last residence); verify before print.
Lessons: AM4.33 The Immigrant Ledger: read the sourcePreview AM4.34 The Immigrant Ledger: map it / time itPreview AM4.35 The Immigrant Ledger: two sources disagreePreview
Supplement: DHS Yearbook of Immigration Statistics
City and country: flows in and out
In 1820 about seven Americans in a hundred lived in a town of 2,500 or more. By 2020 it was eighty. The pies show the urban share at the same marquee dates.
1820
1870
1890
1910
1950
1975
1995
2025
Urban is defined as the Census of each year defined it (changed in 1950 and 2020); 1975 and 1995 are read from the neighboring censuses; 2025 shows 2020.
The great flows
Farm to factory
1870–1920. Mechanized farming needed fewer hands; mills and offices needed more. Rural children and European immigrants met in the same industrial cities. Incomes: a factory wage beat farm labor, but rents and disease were city costs.
The Great Migration
1910–1970. About six million Black Southerners left the rural South for Chicago, Detroit, New York, Philadelphia, Los Angeles and Oakland. Wages roughly doubled for many movers; segregation and redlining shaped where they could live.
Suburbanization
1945–2000. Highways, mortgage insurance and the baby boom moved middle-income white families out of central cities. Suburbs held about a quarter of Americans in 1950 and about half by 2000. Central cities kept the poorest and the richest.
Back to the country?
The 1970s “rural rebound,” and again after 2020 with remote work, rural counties gained people by migration. Rural America is older (median age in the low 40s, against the high 30s in cities) and earns less: rural household incomes run roughly a fifth to a quarter below metro incomes.
Back to downtown
Since about 2000, young graduates and empty-nesters have returned to central business districts, raising residential towers where offices once stood. Small households, high incomes, few children: a demographic recipe for vertical living.
Lessons: SO1.17 Park, Burgess and the concentric zonesPreview AM4.42 The Immigrant Ledger: now, todayPreview
Supplements: U.S. Census Bureau: urban and rural · USDA ERS: rural economy and population · City growth models (companion page)
The great debates: more people, less to go around?
Every theory here answers one question: does population growth exhaust resources, or does it produce the ideas that stretch them? Read them as a running argument across two centuries.
Thomas Malthus
Population grows geometrically, food arithmetically. Unless people marry late and have fewer children, famine, disease and war will hold numbers down.
- Right about pre-industrial Europe, where wages fell when population rose.
- Wrong about what came next: the Industrial Revolution let output outrun births.
Ester Boserup
Malthus backwards: population pressure causes farming to intensify. Crowding pushes people from fallow fields to multiple cropping, irrigation and plows.
- Necessity drives invention; density is a cause, not only a result.
- Critics: intensification can mean more work for the same food per person.
Demographic transition
Societies move through four stages: high births and deaths; falling deaths with high births (boom); falling births; low births and deaths. The US passed through all four.
- Explains the rising median age in Section 1.
- A fifth stage, births below replacement, now describes much of Europe and East Asia.
Paul Ehrlich
“The battle to feed all of humanity is over”: hundreds of millions would starve in the 1970s and 1980s.
- The Green Revolution (Borlaug's wheat and rice) doubled yields instead.
- Famines that did happen were mostly failures of politics, as Amartya Sen showed.
Garrett Hardin
Shared resources get overused because each user gains the benefit and shares the cost. Freedom to breed, he argued, is a commons.
- Elinor Ostrom (Nobel, 2009) found communities that manage commons well for centuries.
Meadows et al.
A computer model of population, food, industry, pollution and resources: on business-as-usual paths, overshoot and collapse in the 21st century.
- Still debated: some later checks say the standard run tracks the data; critics say it ignores prices and substitution.
Julian Simon
People are the ultimate resource: more minds mean more inventions, and scarcity raises prices that spur substitutes.
- The wager: Simon bet Ehrlich that five metals (copper, chromium, nickel, tin, tungsten) would be cheaper in 1990. All five fell; Ehrlich paid.
- Rerun the bet over other decades and Ehrlich sometimes wins.
Michael Kremer
From one million BC to 1990, growth rates rose with population size: bigger populations had more inventors. Separated regions confirm it: larger landmasses advanced faster.
- The idea-based case for density, and a case for cities.
Richard Easterlin
Small generations have it good (scarce workers, high wages) and so have big families; big generations face crowded labor markets and have fewer children. Fertility cycles.
- Explains the boom of the 1950s and the bust that followed.
Ronald Lee & the dividend
When births fall, a country briefly has many workers and few dependents, a window for saving and growth. Then the window closes as the workers retire.
- East Asia used its window; the US is past its own.
The city question: Malthus saw crowding as a danger. Boserup, Simon and Kremer see density as a source of invention. Every central business district is a bet on the second view: more people per acre, more ideas per hour.
Lessons: E22.8 Population, statedPreview E22.6 Two pyramids, comparedPreview
Supplement: Malthus, An Essay on the Principle of Population (1798), full text
In the classroom
- Read the relay. Using the eight origin pies, have students name the leading origin in each year and one law or event that explains the change (the Irish famine, the 1882 Chinese Exclusion Act, the 1924 quotas, the 1965 Act).
- Births or boats? Give the decade table and ask: why is “arrivals ÷ growth” an upper bound? What else would you need to measure net migration?
- Rerun the wager. Students pick five commodities and look up 2015 and 2025 prices adjusted for inflation. Who would have won, Simon or Ehrlich?
- Age and the skyline. Connect Section 1 to the city: what housing does a country with a median age of 17 build, and what does a country at 39 build?
- Debate. Pair Malthus with Boserup, Ehrlich with Simon. Each side gets three minutes and one piece of evidence from this page.
Use the Whiteboard view button at the top for projection: large type, high contrast.
Drawer, lessons, quiz and game
Drawer: People, Ages and Arrivals: Births or Boats? (code 4Q64V9) · This page: code RSV7VJ
Quiz: 10 questions, scored on submit (code BMGB9W)
Game: Births or Boats? drawer game (opens when the drawer goes live) · arcade: Go Fish: The Population Pier
Lessons: APHG 2 · The transition machinePreview E22 2 · The transition's stagesPreview AM4 34 · The Immigrant Ledger: Map it / time itPreview
Page · RSV7VJ
Quiz · BMGB9W
Drawer · 4Q64V9
Sources
- U.S. Census Bureau, decennial census counts 1820–2020 and Vintage 2024 population estimates; census.gov/programs-surveys/popest.
- U.S. Census Bureau, median age by census, and “Nativity of the Population, 1850–2000” (Gibson & Jung, Working Paper 81, 2006); American Community Survey 2023 for the latest foreign-born share.
- U.S. Department of Homeland Security, Yearbook of Immigration Statistics, Tables 1 and 2; ohss.dhs.gov/topics/immigration/yearbook.
- U.S. Census Bureau, urban and rural population, 1790–2020; census.gov urban-rural.
- USDA Economic Research Service, Rural America at a Glance (rural/metro income and age); ers.usda.gov.
- Malthus (1798); Boserup (1965); Thompson (1929); Notestein (1945); Ehrlich (1968); Hardin (1968); Meadows et al. (1972); Simon (1981); Kremer, Quarterly Journal of Economics 108:3 (1993); Easterlin (1980); Lee & Mason, Population Aging and the Generational Economy (2011); Ostrom, Governing the Commons (1990); Sen, Poverty and Famines (1981); Wilkerson, The Warmth of Other Suns (2010).