From the Bureau of Labor Statistics:
In 2015, 78.2 million workers age 16 and older in the United States were paid at hourly rates, representing 58.5 percent of all wage and salary workers. Among those paid by the hour, 870,000 workers earned exactly the prevailing federal minimum wage of $7.25 per hour. About 1.7 million had wages below the federal minimum. Together, these 2.6 million workers with wages at or below the federal minimum made up 3.3 percent of all hourly paid workers.
The percentage of hourly paid workers earning the prevailing federal minimum wage or less declined from 3.9 percent in 2014 to 3.3 percent in 2015. This remains well below the percentage of 13.4 recorded in 1979, when data for hourly-paid were first collected on a regular basis.
This report presents highlights and statistical tables describing workers who earned at or below the federal minimum wage in 2015. The data are obtained from the Current Population Survey (CPS), a national monthly survey of approximately 60,000 households conducted by the U.S. Census Bureau for the U.S. Bureau of Labor Statistics (BLS). Information on earnings is collected from one-fourth of the CPS sample each month.
The CPS does not include questions on whether workers are covered by the minimum wage provisions of the federal Fair Labor Standards Act (FLSA) or by individual state or local minimum wage laws. The estimates of workers paid at or below the federal minimum wage are based solely on the hourly wage they report, which does not include overtime pay, tips, or commissions.