This year, the United States has fallen in the rankings to 10th. Here's Heritage's reasoning:
The United States’ economic freedom score of 76.3 drops it to 10th place in the 2012 Index. Its score is 1.5 points lower than last year, reflecting deteriorating scores for government spending, freedom from corruption, and investment freedom. The U.S. is ranked 2nd out of three countries in the North America region, and its overall score remains well above the world and regional averages.
The U.S.' place now sits behind such economic luminaries as Singapore, Mauritius and Chile. The top three countries by ranking - Hong Kong, Singapore and Australia - gained in their position relative to most of the others in the top ten.
The Index is a very, very interesting look at economic freedom around the world. There are many countries that may surprise people how free that Heritage ranks them, like Switzerland, Denmark and Bahrain. On the other hand, the country that comes in last place will surprise no one: North Korea.