Austin is the best city in the country to start a small business, according to a Portfolio.com/bizjournals study.

The Portfolio study analyzed the nation’s 100 largest metro areas, looking for the places that are most conducive to the creation and development of small businesses.

The highest scores in the study went to areas that have prosperous economies, are expanding rapidly, and are densely packed with small businesses. A small business is defined in the survey as any private-sector employer with 99 or fewer employees.

Despite the recession, Austin experienced impressive population, job and small business growth. The number of small businesses in the Texas capital increased 5.6 percent between 2006 and 2007, the latest period covered by official statistics. The typical metro area experienced small-business growth of 1.4 percent, said Portfolio.

The most promising region for entrepreneurs is the South, which is home to 12 of the 20 best metros for small businesses, according to Portfolio.

Rounding out the top five cities are Baton Rouge, La.; last year’s top city, Raleigh, N.C., came in third; Charleston, S.C. was fourth; and Portland, Maine was fifth.

Detroit came in last in the small-business rating, along with Youngstown, Dayton, and Toledo, Ohio, and Milwaukee.