Us Population in 1914 was 99,111,000. http://www.census.gov/population/estimates/nation/popclockest.txt

20,000,000 + people immigrated to the US between 1870-1910. http://www.yale.edu/ynhti/curriculum/units/1988/2/88.02.03.x.html So at least 20% of the population had traveled 1000's of miles to the to the US from another country. In 1914 there was an extensive railroad network in the US. There was also a good deal of internal migration, as people moved west to work in agriculture and mining and to northern industrial centers.

Great observations on the part of /u/used-books and /u/HallenbeckJoe. Clearly, things could be a mixed bag. Immigration and war provided the means for hundreds of thousands to travel long distances. But for the ones who were in an American home, and who did not go to war, the story could be remarkable sedentary. In the mid 1980s I conducted an oral history of someone who was born in 1918 in central Iowa. I asked particularly about how far he and his family had traveled before the Great Depression. His father, a successful hog farmer and speculator, was known to travel to Chicago for trading, but for the rest of the family, the extent of travel consisted of several trips to Ames and Marshalltown, both about 30 miles from the farm. The family seemed not to go to the Iowa state capital, Des Moines, approximately 45 miles away. During the late 1800s, part of the family had settled in Winter South Dakota, and so parts of the Iowa family traveled there to visit them, but the entire family did not go because maintaining the farm and all the livestock was a requirement of life on the farm.

My informant began truck driving in 1937 after graduating from high school. Suddenly, the world was open to him, and he went to Chicago on a weekly basis. The world was changing, and part of this was the creation of a new system of roads that allowed for the travel. He also went to war, so he traveled to Europe, which none of his elder siblings ever did. The least traveled of his siblings probably traveled no more than 200 miles; the more traveled went 1,000 miles to Salt Lake City before WWII, but all of this happened between 1925 and 1939. The Lincoln Highway had opened things up in a way that was clearly not the case earlier.

I'm afraid I can't comment on that fact, except for saying that 20 miles seems questionably low. But I can remind you that lots of Americans traveled thousands of miles from home as soldiers around that time. In 1898, during the Spanish-American War, tens of thousands American fought in Cuba and Puerto Rico. In the years after 1899, over a 100,000 Americans traveled as far as the Philippines, when they served in the military during the Philippine-American War. Obviously, during WWI, millions of Americans went to Europe. But this "fact" might be older than the centenary of the First World War. Were these "average Americans"? Probably not, but they did represent a large portion of the U.S. population at the turn of the century.