Apple became the first U.S.-listed company in history to achieve a $1 trillion market capitalization on Thursday. U.S. Steel is generally cited as the first U.S. publicly listed company to reach a $1 billion market capitalization, immediately upon going public in 1901.
IBM is sometimes identified as the first publicly listed U.S. company to reach the $100 billion milestone, doing so on August 20, 1987. However, IBM never closed above that threshold. Meanwhile, AT&T Corp. closed above $100 billion in November 1992, according to FactSet.
A cautionary tale: On July 16, 1999, Microsoft became the first U.S. company to reach a market cap of $500 billion. It stayed above $500 billion for just two trading sessions before dipping back below that level. This was, of course, the heyday of the dot-com boom. Microsoft went on to again hit $500 billion in market value, eventually reaching $607 billion in market cap, in December 1999. But in the spring of 2000, the bubble popped — and Microsoft finished that year with a market cap of $231 billion.