The federal minimum wage peaked in 1968 at $8.68.
"Adjusted for inflation, the federal minimum wage peaked in 1968 at $8.68 (in 2016 dollars). Since it was last raised in 2009, to the current $7.25 per hour, the federal minimum has lost about 9.6% of its purchasing power to inflation. Back in 2015, The Economist estimated that, given how rich the U.S. is and the pattern among other advanced economies in the Organization for Economic Cooperation and Development, “one would expect America … to pay a minimum wage around $12 an hour.”"
Source: http://www.pewresearch.org/fact-tank/2017/01/04/5-facts-about-the-minimum-wage/