Apologies for the outdated data - I made this a couple years before the 2010 Census data came out. Props to anyone who feels like updating it.
Note that the Census defintion of “Urban” probably does not map closely on to the average person’s conception of urbanness. It is generally based on population density, but the low threshold includes many areas that most people would call “suburban.” For the specific critera used, see page 5 here.
California and New Jersey are tied for the rank of largest non-rural populations (94.4% urban), while Vermont has the smallest proportion of urban residents (38.2%). Not surprisingly, most of the smaller East Coast states that contain major cities rank fairly high. But even much larger states with very high proportions of agricultural land, like Illinois and Texas, have populations that are remarkably concentrated in cities.
It’s interesting to note that the percentage of urban population is not a great indicator of population density. Nevada - the 43rd most densely populated state in 2000 - had the 3rd most urban population. By contrast, a relatively densely populated state like North Carolina (17th densest in 2000), only ranked 39 in urban population. Obviously, the lack of water and arable land in the Southwest means that most people live in urban clusters by necessity.
Only four states have a rural majority. In 1950, that number was nineteen.