Same thing probably happened during the last depression. Nothing unsual considering the economy.
Unfortunately, this particular bls.gov data set only goes back to 1948. Still, it shows no crazy lying chicanery like what the lefties are trying to pull starting in 2008.
The data says "Civilian labor force" so, call me a moron, but to me that means all people who can work. BTW, this graph is in thousands, so basically, b>the missing population - extrapolating the graph - is about 30 million people.