In America, getting on in the world means getting out of the world we have known before.
-- Ellery Sedgwick, The Happy Profession, 1946
America is a nation of people forever running toward bright new futures -- or away from bleak presents and past failures. Every decade since 1790, the U.S. Census has given demographers and historians a chance to take stock of this restless population and chronicle its hopes and fears.
A century ago, Frederick Jackson Turner used the 1890 headcount as a springboard for his provocative "frontier thesis," which argued that America's distinctive culture was the result of its...