What To Learn From 150 Years Of The S&P 500 Share Share Trending In 1956, Standard & Poor created a new stock market index. Composed of the top 500 (or so) individual company stocks in the U.S. stock market and weighted according to their market capitalization within the index, the index itself has become the standard gauge of the larger U.S. stock market. 2021 marks the 65th year the S&P 500 daily stock market index has been in existence. But the index has a deeper history. In 1928, Standard Statistics Bureau, one of the pre-merger companies that later became today's Standard & Poor, created a daily composite stock market index made up of 90 individual stocks of U.S. corporations, with historical data going back to 1925 to provide some built-in history for the new index. The combination of 50 industrials, 20 railroads, and 20 utility companies provided one of the first broad measures of the U.S. stock market, expanding beyond the 30 industrial firms covered by the Dow Jones Industrial Average. Around the same time, Standard also created a weekly index to track the collective stock market performance of 500 U.S. companies, which is eventually what took over in 1956 as a daily index.