The survey put Real Madrid in second spot, valued at 3.26 billion dollars. The New England Patriots and baseball's New York Yankees were next, each worth 3.2 billion dollars, while reigning European champions Barcelona were the fifth most valuable team, with an estimated worth of 3.16 billion dollars.
The Cowboys, who made a record NFL revenue of 620 million dollars last season, also sit atop the list of richest NFL teams for the ninth year in a row.
They're often described as "America's Team" despite not having won the Super Bowl since 1995.
Their worth is understood to have shot up thanks to the NFL's lucrative domestic television deal.