"The corrections sector is a large and growing part of the labor force. According to the Census Bureau, more than 770,000 people worked in the U.S. correctional industry in 2008.60 The U.S. Department of Labor, in its 2010-11 Occupational Outlook Handbook, estimates there were about 620,000 guards, probation officers, prison supervisors and court bailiffs in 2008.61"

Source

Kirchhoff, Suzanne M., "Economic Impacts of Prison Growth," Congressional Research Service, (Washington, DC: Library of Congress, April 13, 2010), p. 12.
http://www.fas.org/sgp/crs/mi…