The federal minimum wage rate will increase on July 24th from $5.85/hour to $6.55/hour. As employers are required to pay the higher of the federal and state minimum wage, only employers in states with a minimum wage lower than $6.55 will be affected by this. The federal tipped minimum wage, currently $2.13/hour, is not changing.
Information on state minimum wages is available on the US Department of Labor's website.