Flint in Michigan was considered as America's most dangerous city in 2011. With a population of 109,245, the rate of Violent Crime Per 1,000 is 22, the rate of assault per 1,000 residents is 14.6, and the number of murders in 2010 is 53.
Detroit in Michigan was the second dangerous city in America, followed by St. Louis, New Haven and Memphis.
You can also check the United States cities by crime rates here.
Source: http://www.theatlantic.com