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BHistory
History · Ajo

Ajo’s post office opened in 1900, and 15% of its homes were built before 1940

More historic than 58% of U.S. towns · #10 of 140 in Arizona. What drives it

3 places in town are on the National Register, among them a historic district with 106 buildings. Below: 3 old photos and papers, maps from 1932 on, and the census since 1920.

1900first post office
3on the National Register
15%homes built before 1940
3old photos & papers
1famous people
Add an old photoShare a memory
From Ajo’s archive · credits on each photo
Quick answers

How Ajo began

When was Ajo founded?

1900

The Ajo post office opened in 1900, the earliest record of the town by name.

First census: 2,336 in 19202020 census: 3,039126 years

How historic is Ajo?

B

More historic than 58% of U.S. towns, on its age, its old homes and the National Register.

What drives the grade ↓
Founding year: the first Ajo post office (Blevins & Helbock, CC0).The full story ↓
History grade

What drives Ajo’s History grade

On its age, its old homes and the National Register, Ajo is more historic than 58% of U.S. towns, #10 of 140 in Arizona. Its National Register listings hold the grade up; its age pulls it down.

B
HistoryA character grade: shown, never part of Ajo’s overall grade.
Founding era1900, from the first post office: founded 1900–1944, an older era than 9% of U.S. townsDHomes built before 194015.0% of homes (±5.1) · typical AZ town 0.4% · U.S. 8.4%BNational Register3 listings, 113 historic buildings, 364 per 10,000 residents · typical AZ town 0.1 · U.S. 2.4A
All U.S. towns we grade (21,289)Ahead of 58%
NewerOlder
Arizona towns of 2,500+ (140)Ahead of 94%

Few Arizona towns list much on the Register (a typical Arizona town has 0.1 per 10,000 residents, the U.S. 2.4), so Ajo’s 364 sits above most of its state (98% of Arizona towns have fewer) while its 113 historic buildings outnumber those of 90% of U.S. towns.

How sure. Graded on any two of the three inputs instead, the letter would range from C to A. The pre-1940 share is a Census survey estimate (±5.1 points). The founding year is the first post office, not a stated founding date.

Founding year: the first post office (other dates in Quick answers). Homes: Census ACS 2020–24. National Register: National Park Service, May 2026 list; each listing counted once (boundary changes and added documentation belong to their listing), and a historic district counts its contributing buildings. How TownRatings grades history →

What stands out about Ajo’s past

Read from the archive, the National Register and the record. The page puts what stands out first.

A history waiting to be writtenOnly 3 old photos are in the public archives. The rest are in attics and albums.A historic districtThe Ajo Townsite Historic District takes in 106 historic buildings.Boom and bustPeaked at 7,049 in 1960; 3,039 people lived here in 2020.Old housesHalf of Ajo’s homes were built before 1959.
★ What stands out · Help out

Start Ajo’s collection

The first neighbors to add old photos shape how Ajo’s history is told.

Decades since 1900 with photos
00s10s20s30s40s50s60s70s80s90s
1 of 10 decades. The empty ones are waiting for someone’s album.
Date a photo2 archive items have no date. Guess the decade.+2Retake an old viewDeparting: stand where they stood+15Share a family photoSign in to add one+10
On the National Register

3 listings protect 113 historic buildings

The country’s official list of buildings and places worth saving.

places listed
3
National Historic Landmarks
0
none yet
historic buildings protected
113
each building in a district counts
first listed
1998
John and Isabella Greenway House
John and Isabella Greenway HouseAjo Townsite Historic DistrictCurley School
BuildingsDistricts

Architectural styles listings

Late 19th and 20th Century Revivals2
Pueblo Revival1
Late 19th and Early 20th Century American Movements1
Vernacular1
Mission/Spanish Colonial Revival1
John and Isabella Greenway HousePueblo Revival
Ajo Townsite Historic DistrictLate 19th and Early 20th Century American Movements
Curley SchoolLate 19th and 20th Century Revivals

National Park Service, National Register of Historic Places. Photos from Wikimedia Commons, credited on each place’s page.

People over time

Ajo, census by census

05001,0001,5002,0002,5003,0003,5004,0004,5005,0005,5006,0006,5007,0007,500192019401960198020002020Peak: 7,049

Peaked at 7,049 in 1960; 3,039 people lived here in 2020.

10 censuses, 1920–2020.

U.S. Census Bureau decennial counts, from the census table on Ajo’s Wikipedia page.

The story

How Ajo came to be

From Wikipedia’s history of Ajo.

Read it all →

Ajo is the Spanish word for garlic (Spanish pronunciation: [ˈaxo]). The Spanish may have named the place using the familiar word in place of the similar-sounding Oʼodham word for paint (oʼoho). The Tohono Oʼodham people obtained red paint pigments from the area.

Native Americans, Spaniards, and Americans have all extracted mineral wealth from Ajo's abundant ore deposits. In the early nineteenth century, there was a Spanish mine nicknamed "Old Bat Hole" that was abandoned due to Indian raids. Tom Childs Sr., found the deserted mine complete with a 60-foot (18 m) shaft, mesquite ladders, and rawhide buckets in 1847. He did not stay long at that time because he was on his way to the silver mines near Magdalena de Kino.

Text from Wikipedia, licensed CC BY-SA 4.0.

Timeline

Ajo, 1900 to 1974

Woven from the archive, old maps, post office records, the National Register and the people born here.

  1. 20th century
  2. 1900Post officeThe Ajo post office opens
  3. 1932On the mapFirst mapped by the U.S. Geological Survey
  4. 1959Born hereFrank Kalil is born here
  5. 1960CensusPopulation peaks at 7,049
  6. 1974In the archiveDeparting
By decade

Ajo, decade by decade

One decade in the archive so far: the 1970s. Scroll each row; tap a photo for its story.

1970s1 item
Departing1974Departing
1980s–1990snothing yet
Nothing in the archives for these yearsWeddings on Main Street, storms, parades, school pictures, the old store. If it’s in your family album, it belongs here.
Add from your album
Date unknown2 to date
Hocker Well, JacalDate?Hocker Well, JacalBates Well, Jacal, Growler WashDate?Bates Well, Jacal, Growler Wash
Today9 recent
A mountain koo2022A mountain koo100 Estrella Restaurant2017100 Estrella RestaurantThe neighbors invited us for barbecue!2012The neighbors invited us for barbecue!Atop2012AtopNot Bulldozed2011Not BulldozedDaffodils in2011Daffodils inAjo Hilltop2011Ajo HilltopDowntown2010DowntownRefuelers Keep Southwest Border Aviation in the Sky DVIDS572282007Refuelers Keep Southwest Border Aviation in the Sky D…
On the map

Ajo on the map, 1932 to 1990

Every edition of the U.S. Geological Survey’s map of Ajo. Tap a year, or press play to watch the town change.

Ajo on the 1932 USGS mapAjo on the 1963 USGS mapAjo on the 1990 USGS map1932Ajo sheet · 1:62,500

U.S. Geological Survey historical topographic maps (public domain), via Esri’s collection of the scans. The red ring marks the center of Ajo.

Then & now

Stand where they stood

No then-and-now pairs yet. Take a photo from the same spot as an old one and they appear here side by side.

Departing
Retake this viewDeparting, 1974

Find the spot, match the angle, and add your photo. It becomes the first then-and-now pair on Ajo’s page.

Retake this view · +15
Places that used to be

Old corners, places now gone and burying grounds

Ajo’s post office has been open since 1900.

Hamlets and corners on the map
ChildsGibsonMexican Town
Gone or out of use
Ajo Army Air FieldmilitaryAjo Copper MinesmineNew Cornelia Branch HospitalhospitalNew Cornelia Minemine
1cemetery inside Ajo
Ajo

US Post Offices dataset (Blevins & Helbock, CC0). Places and cemeteries from the USGS Geographic Names Information System (2021).

Questions about Ajo’s history

What year was Ajo founded?

The Ajo post office opened in 1900, the earliest record of the town by name (U.S. post office records).

How does Ajo rank for history?

Ajo is more historic than 58% of U.S. towns, #10 of 140 in Arizona. The History grade combines the town’s founding era, the share of homes built before 1940 and its National Register listings. It’s a character grade, so it isn’t part of the overall grade. How it works.

What is on the National Register in Ajo?

Three places: the John and Isabella Greenway House (listed 1998), the Ajo Townsite Historic District (2001) and the Curley School (2008).

How old are the homes in Ajo?

15% of Ajo’s homes were built before 1940 (Census estimate, ±5.1 points), against a typical 0.4% for an Arizona town; the median home was built in 1959.

Memory lane

What the archives can’t tell you, neighbors can.

Town Square →
Start a conversation
Sources

Where this page comes from

Founding dates: Wikidata, Wikipedia, the U.S. post office records of Blevins & Helbock (CC0) and the Census. Homes by year built: Census ACS 2020–24. National Register of Historic Places: National Park Service (list of May 22, 2026). Old photos, postcards and papers: Wikimedia Commons, the Library of Congress and other public archives, credited on each item’s page. Maps: U.S. Geological Survey historical topographic maps (via Esri) and Sanborn fire-insurance maps (Library of Congress). History text and census tables: Wikipedia (CC BY-SA 4.0). Places that used to be: USGS Geographic Names Information System (2021).

From Wikimedia Commons (10), the Library of Congress (2), the National Register of Historic Places (3), Wikipedia, Wikidata and Wikipedia for famous people, U.S. Geological Survey historical maps, U.S. Census counts (via Wikipedia), the US Post Offices dataset (Blevins & Helbock) and the USGS Geographic Names Information System. Archive images are copied here with their credits and licenses, shown on each photo’s page. Refreshed monthly.