1. Gerald Cavendish Grosvenor & family

• Net Worth: 11.4 B                                                                 
• Source of Wealth: Real state, inherited, growing
• Citizen: United Kingdom
• Age: 61

The continued success of London's booming prime property market meant a good year for Gerald Cavendish Grosvenor. The U.K.'s wealthiest landowner, also known as the 6th Duke of Westminster, saw his fortune rise $400 million this past year along with the value of real estate in Belgravia, London's most expensive neighborhood, where his family trust owns 190 acres (and where homes can sell for $150 million). His private Grosvenor Group separately owns real estate on five continents and reports just under $20 billion in assets under management. His family also has 96,000 acres in Scotland, 32,000 acres in Spain and thousands elsewhere in England.