The Bureau of Labor Statistics maintains occupational employment statistics showing estimates for employment and wages for security guards in the U.S. and by state and major metropolitan areas.
The site indicates that there are more than 1,000,000 security guards employed throughout the country, with a mean annual wage of $27,550. The annual wage varies, with those at the 10% percentile having an annual wage of $17,500, and those at the 90% percentile having an annual wage of $43,150.
About 2/3 of all security guards are employed in the “investigation and security services” industry. Primarily that consists of jobs with investigation, guard and armored car services,
Security guards fall within the umbrella classification of the “protective service occupations:. Protective services occupations also includes local and state law enforcement. There are over 3,000,000 people employed in the protective service occupations, including both security guards, law enforcement and related occupations.
See http://www.bls.gov/oes/current/oes339032.htm for more information about employment and wages for security guards.