Geographic concentration in U.S. hog production from 1974-96 is investigated using a measure based on Theil's entropy index. For the U.S. as a whole, geographic concentration is occurring at a slow rate, both for hog farms and hog numbers. However, for particular states, primarily in the new Southern Atlantic production region, concentration is high and increasing at a rapid pace. Concentration was increasing for the 23-year period for 16 out of the 20 states in the analysis. Results indicate that geographic concentration by augmentation is occurring to the greatest degree in Arkansas, Missouri, North Carolina, Oklahoma, and Pennsylvania.