The City of Pensacola shrank last decade, dropping 8 percent from 56,255 in 2000 to 51,923 in 2010. Detroit, Michigan saw its population drop a whopping 25 percent. It was the largest percentage drop in history for any American city with more than 100,000 residents (aside from New Orleans post-Katrina). According to the NY Times, the number of people who vanished from Detroit — 237,500 — was bigger than the 140,000 who left New Orleans. Read more.