Given the current recession, its hard to avoid the irony in this: The two richest women in America have Wal-Mart to thank for their billions.

Alice Walton is the daughter of Wal-Mart founder Sam Walton. Christy Walton is Sam's daughter-in-law. Each has a net worth of $23.2 billion, thanks to the ubiquitous discounter, America's largest employer.

Alice has a taste for objects you can't find in any Wal-Mart: fine art. She's led her family in hundreds of millions of dollars in donations to the Crystal Bridges Museum. The new art museum will open in 2010 in Bentonville, Ark., the location of Wal-Mart's headquarters.

Christy is the widow of Wal-Mart heir John Walton, who died in a 2005 plane crash. She also is using some of her considerable fortune for art. She recently donated an award-winning yurt--a domed tent used by Asian nomads--to a San Diego museum.

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They're just two of the 42 women on our 2008 list of the 400 richest Americans, a rarefied group with a combined net worth of just over $181 billion when we calculated their fortunes at the end of August.

Abigail Johnson ranks as the third wealthiest woman on our rich list with a fortune of $15 billion. The 46-year-old Boston resident helps run Fidelity Investments--the family business and America's largest mutual fund company.

Abigail's grandfather Edward C. Johnson II founded the company in 1946. Her father, Edward C. Johnson III, has served as chief executive and chairman of the company since 1977.

Abigail could be the next to take the helm. Last year's departure of several top Fidelity executives fueled talk that Abigail will succeed her father. She certainly has the experience for the position. Abigail started running her first diversified fund in 1993. She became president of the company's mutual fund division in 2001. Now she runs Fidelity's personal and workplace investing division.

The youngest female billionaire in the U.S. is Margaret Magerko. Her father founded the building materials supplier 84 Lumber in 1956. Thirty-six years later, it was Maggie's turn to take the helm.

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She let Home Depot and Lowe's grab the do-it-yourself home improvers. 84 Lumber instead went after contractors and developers. Slowing home building is sapping company sales this year but Magerko is still comfortably in the billion-dollar club. We estimated the 42-year-old's net worth at $1.7 billion in our Forbes 400 list.

Like many of the men on the Forbes 400 list, most of the women made their fortunes the old-fashioned way: through inheritances. But some did it all by themselves. Talk show titan Oprah Winfrey was born in rural Mississippi. When her parents split, she shuttled between various households, living on a pig farm at one point.

Despite the fractured family, Winfrey excelled in school. She decided on a career in media and pursued it with an unwavering determination. Winfrey began working as a radio DJ while still in high school. By 19, she was anchoring a local Nashville, Tenn., news show.

In 1984, she moved to Chicago to host a morning talk show. Her accessible demeanor and ability to empathize with guests drew increasingly large audiences. Now her show airs in 141 countries and draws 46 million viewers a week in the U.S. alone. Forbes estimated the Mississippi farm girl's net worth at $2.7 billion in August.

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