The wealth of affluent American families grew substantially in 2006, with 1.14 million households now stating a net worth of $5 million or more, according to Affluent Market Insights 2007, a report released April 17 by Spectrem Group. It is the first time that the number of ultrahigh-net-worth households has topped 1 million.

The survey shows that 15 million households in the United States fall into the affluent category—$500,000 to $1 million in investable assets. Another 9 million households indicated worth of $1 million or more, in addition to the 1.14 million ultrahigh-net-worth families. The number of $5 million–plus households was up 23 percent over 2005, and has quadrupled in the past 10 years, according to Catherine S. McBreen, managing director of Spectrem Group.

“The past few years have been nothing short of astounding for wealthy Americans,” McBreen said.

The report is based on a survey done in July 2006.