The overall number of millionaire households in the U.S. has increased nationwide for the second time in two years. In 2011, there were 5.94 million millionaire households, compared with 5.56 million households a year earlier, an increase of approximately 6.8 percent. Nearly every U.S. state saw an increase in its total number of millionaires, adding thousands of households to millionaire status, according to the new numbers from Phoenix Marketing.