In real terms, the Federal minimum wage has varied within $0.60 / hour of its current level in the last thirty years.
The percent of hourly workers earning Federal minimum wage or less has steadily declined from 6.5% in 1988 to 2.3% in 2017. This could drop below 2% in 2018.
Source: FRED
If terms of number of workers, it looks like this:
There are about 155 million employed persons in the US. Of these, 80 million are hourly workers.
Of all workers, about 2.2 million earn the Federal minimum wage or less.
However, about 1 millon of these are under the age of 24, and half of those are age 19 or less.
Only 882,000 full time workers earn minimum wage or less. And of these, 700,000 earn less than minimum wage, that is, the vast majority of these are in businesses with tips, ie, waiters.
Only 183,000 workers work full time and earn minimum wage. Thus, the notion that there is some large cohort of adult, full time workers not in businesses with tips who earn the minimum wage is simply untrue. Only about 1 in every 1,000 employed persons in the US is both working full time and earning minimum wage without tips.