Positive economic data, such as better employment numbers, healthy retail sales, housing starts and better-than-expected earnings, have lifted the S&P 500 near its all-time high from 2007.
Additionally, the Federal Reserve has maintained its quantitative easing plan to buy bonds as a way to keep rates down and stimulate the economy.
Meanwhile, financial problems in Europe have abated, boosting confidence in the euro.
However, the month ended on a dour note after the U.S. government revealed an unexpected fourth quarter contraction in the economy.
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Max Chen contributed to this article.