Fewer than 1% of American farms are organic, and generated $3.16 billion in sales in 2008, the U.S. Agriculture Department found in its first in-depth survey of organic farming.

The USDA said Wednesday that it tallied 14,540 organic farms and ranches that were either certified by the USDA or exempt from those rules because their annual sales fell below $5,000.

While organic products have been one of the hottest growing areas in the supermarket, the USDA survey found that they were still a tiny enterprise in the farm belt.

For example, USDA-certified organic farms use just 4.1 million acres of land. In its 2007 agriculture census, the agency counted a total of 2.2 million U.S. farms of all types and sizes using 922 million acres of land.

The USDA conducted the organic farming survey in part to establish a baseline for tracking the health of the sector, which doesn't yet produce enough to satisfy all domestic needs. While U.S. consumers are willing to pay a premium price for organic products, some U.S. food companies must import organic ingredients from overseas, such as soybeans from China.

Among other things, the USDA survey found that California is the biggest organic farming state, with 20% of the nation's operations and $1.15 billion in 2008 organic sales.

Write to Scott Kilman at scott.kilman@wsj.com