The S&P closed above its all-time record high set in October 2007 before the financial crisis, while the Dow Jones industrials hit yet another record close.
Though the Dow is the most widely watched U.S. stock index, the S&P is followed closely by professional investors as its made up of many more stocks and represents a diverse mix of companies.
Like the Dow, the S&P wiped out more than half of its value during the recession.
Since the Dow broke through its record high three weeks ago, investors have been closely watching the S&P for a similar breakthrough.
The Federal Reserve's policies are among the reasons behind recent highs. Low interest rates mean money moves into the stock market, as it is one of the few available investment options.