The historical values of the Standard & Poor's 500 index are available online through resources such as CNN.com and Yahoo.com's finance site. Yahoo! Finance allows users to access information for the index's history as far back as the mid-20th century.
Yahoo.com allows users to download the full data range of a stock or index's value since its initial listing in spreadsheet format. Opening, closing, high and low values for the stock or index's trading price are amongst the data provided on Yahoo! Finance. Users can also compile this information in weekly and monthly intervals and can set a custom range of dates to download prices. Similar services are also available on sites such as Bloomberg.com and Morningstar.com.