McMahon As An Irish Last Name

This article looks at how common McMahon is as a last name in Ireland and the United States from the 19th century to the present day.

You’ll learn the meaning and origins of the McMahon surname while exploring some notable and famous people that held it.

I use census records, emigration lists, and military archives to uncover fascinating patterns. If you’re studying your genealogy, check out my sources at the end of the post so you can do your own research.

How Common Is McMahon As A Surname In Ireland?

Detailed current statistics about surnames are not publicly released by the Irish government. Instead, they offer the ten most frequently occurring surnames among newborns in the previous year. McMahon

Thankfully, an Irish genealogist named Seán Murphy studied the names in national phone books published in the 1990s. His estimates aren’t as accurate as a census, but they are still a good way to get an estimate of numbers.

McMahon was ranked 35 in the top one hundred names in this decade with a total of 17,300 entries.

This graphic shows how it ranks compared to the 1st, 33rd, 66th, and 100th entries in the survey:

McMahon Ireland 1990s

McMahon In The Early 1900s

The only full censuses that are publically available in Ireland are from 1911 and 1901. Prior decades were either destroyed through government action (to reclaim storage space) or by a catastrophic fire during the Irish Civil War.

So, let’s focus on the early 1900s.

I used online archives to calculate the total numbers by surname. I consider these estimates due to some percentage of transcription errors. So, I’ve rounded the numbers to the nearest fifty.

There were 8,750 residents named McMahon on the island in 1911.

Ten years earlier, McMahon had about 9,100 residents in the 1901 census.

Population Estimates In The 1890s

A study of Irish surnames was conducted in 1890 by the head of the Civil Registrations Office. It was published as a “Special Report on Surnames In Ireland.”

The survey estimated that there were about 10,700 people named McMahon in the country.

Emigration To America After The Irish Famine

The Irish diaspora is large and widespread with a significant number of people emigrating to other parts of the globe. The destinations traditionally have been England, the U.S., Canada, and Australia. Emigrants were driven by various factors like political unrest, poverty, and food scarcity.

The largest wave of emigration to the United States occurred during the 19th century. The peak was in response to the Great Irish Famine, which took place between 1845 and 1852. A plant disease devastated the main food and income crop for much of the population.

I reviewed the McMahon name in the shipping passenger lists arriving in New York during this period. The departures were from both Ireland and England.

This picture shows how the numbers rose and fell in the years after the famine:

McMahon emigration after the famine

How Common Is McMahon As A Last Name In The U.S.?

Based on the 2010 U.S. census, the name McMahon ranks about 892 among Irish names in America with 39,411 bearers.

Although the 2010 census has exact numbers and rankings, the rank I assign here is my estimate. If you’re curious about how I got there, here’s a brief explanation…

Estimating Rank In The United States

Historically, some Irish families with Gaelic surnames took English-sounding names as translations under the influence of colonization.

As these names also have English origins, they will have been brought to the United States by both British and Irish immigrants. Because the census doesn’t ask about specific European origin (e.g. England vs Ireland), it’s impossible to identify the proportion with Irish heritage.

I reviewed the census to identify which names are predominantly Irish in origin. In order to estimate the relative rankings of “Irish” names, I’ve mostly excluded surnames that have varying origins.

McMahon In Historic Times

It is fascinating to examine how the prevalence of a surname shifts over the course of time in a country as young as the United States. As well as immigration, this reflects other demographic shifts across the nation. Factors include higher child mortality rates and longer life expectancy.

The historic census records have been transcribed and digitized. I used online archives to run counts of surname populations.

But the totals can’t be exactly accurate due to transcription errors. So, I’ve rounded the numbers to the nearest 50 in the graph below.

This picture shows the numbers every twenty years from 1860 to 1940:

how common was McMahon in the U.S. between 1860 and 1940

These are the numbers in the graph:

  • 1860: 4,300
  • 1880: 10,950
  • 1900: 16,350
  • 1920: 20,350
  • 1940: 24,600

McMahon In World War II

During World War Two, approximately 8.3 million men and women joined the ranks of the United States Army. Many were of Irish descent. Some had even been born in Ireland and emigrated.

There were registration records for 1,571 soldiers named McMahon who enlisted between 1938 and 1946.

There were 22 who were born in Ireland.

McMahon Surname: Meaning And Origin

McMahon comes from the Gaelic surname “Mac Mathghamhna”. The “Mac” in Irish names literally means “son of”, so the name means “son of Mathghamhain”.

The personal name Mathghamhain derives from two words: maith, which means good, and gamhain, which refers to a calf. However, a “good calf” in Irish is also a term for a bear. So, the full name is akin to “son of the good calf” or “son of the bear”, as “bear” is also a metaphorical meaning of “good calf” in Gaelic tradition.

One early family was a branch of the O’Briens of Thomond. They descended from Mahon, a son of Murtagh Mor O’Brien who was a king in the early 12th century. Another McMahon family was powerful in Ulster in the 14th century, in what is now County Monaghan.

Famous Or Historic People Named McMahon

Here are some notable people with the family name:

  • James McMahon (1856 – 1922): born in County Armagh, he joined Cornell University where he became a professor of Mathematics. He was a prominent mathematician in academic circies.
  • Ed McMahon (1923 – 2009): a Marine Corps fighter pilot who went on to become a household name as a game show host, comedian, and actor. He was best known for his partnership with Johnny Carson.


McMahon As A Last Name

External Research

The Ireland 1990s estimates are from Seán J. Murphy’s research paper.

The population estimates of 1890 are based on the “Special Report on Surnames in Ireland“, published in 1909.

The population figures for the 2010 U.S. Census come from a file provided by the U.S. Census Bureau.

Internal Research

Some of the population numbers are based on my own research and calculations using online archives. I’ve rounded those numbers to the nearest 50 to account for transcription errors and other technical issues with online databases of this type.

The Irish census estimates for 1901 and 1911 are my calculations based on the Irish National Archives

I plotted the emigration figures from 1845 to 1854 based on calculations from the archives of the New York Passenger Lists (1820-1957).