It's official: The longest recession the country has endured since World War II ended in June 2009, according to a group that dates the beginning and end of recessions.

The National Bureau of Economic Research, a panel of academic economists based in Cambridge, Mass., says the recession lasted 18 months.

It started in December 2007 and ended in June 2009. That was the longest of any recession since World War II. Previously the longest postwar downturns were those in 1973-1975 and in 1981-1982. Both of those lasted 16 months.