Anne Cox Chambers, the heiress to the Cox family media empire who went door-to-door campaigning for Democratic politicians, served as ambassador to Belgium during the Carter administration and helped bankroll museums and other causes, died on Friday at her home in Atlanta. She was 100. For more than 30 years Mrs. Chambers and her sister, Barbara Cox Anthony, had controlling ownership of that empire. Her sister died in 2007 at 84. Forbes magazine estimated Mrs. Chambers’s wealth at $12 billion in 2013, the year she dissolved a family trust and gave most of that fortune to her children. Mrs. Chambers was the daughter of James Middleton Cox, who was a three-term governor of Ohio, an unsuccessful Democratic candidate for president in 1920 (he and his running mate, Franklin D. Roosevelt, were drubbed in the general election by the Republican, Warren G. Harding), and the founder of Cox Enterprises. In 1970, she and her husband at the time, Robert W. Chambers, were among the largest supporters of Jimmy Carter’s victorious run for governor of Georgia, giving $26,500. They contributed $39,400 to Mr. Carter’s presidential campaign in 1976. President-elect Carter appointed her ambassador to Belgium, and she resigned her chairmanship of Cox Broadcasting Company to accept. Her involvement in politics continued after her term as ambassador ended in 1981 with the arrival of the Reagan administration. She credited her father for her lifelong affiliation with the Democratic Party. Anne attended Miss Porter’s School in Farmington, Conn., spent a year in Paris and graduated from Finch College in Manhattan, which closed in 1976. She married Louis G. Johnson six months in 1940. That marriage ended in divorce, as did a second marriage, in 1955, to Robert William Chambers. She is survived by two daughters from her first marriage, Katharine Rayner and Margaretta Taylor; a son, James Cox Chambers, from her second marriage; and several grandchildren and great-grandchildren. One grandson, Alex Taylor, is now the president and chief executive of Cox Enterprises.