Playing with Tableau, I created the video below of how the US Mainland slowly become more urbanized over its founding.
It is neat to watch Manifest Destiny in action. We were predominately rural until about 1920. First we moved west until the 1870s. With no more land to take from France, the Indians, and Mexico, we started moving towards cities as we became a more industrialized society. In the 1910s most Americans we in cities as they moved off the farm and into factories.
While the largest in area, the Western States are the most urbanized. This is because there are relatively fewer farms and most people live in a narrow strip by the Pacific Ocean. The South and Midwest are the least urbanized by are slowly catching the other areas. People move into the cities of the South and people leave farming towns of the Midwest for better economic opportunities.
This migration has lead younger people away from rural areas. This as caused the median age of many rural areas to increase.