The Federal Reserve Bank of St. Louis and the U.S. Treasury provide historical data for 30-year Treasury bonds. On the FRED website, peruse the Economic Data section to find a table of rates. On the U.S. Treasury's website, visit the Resource Center to view historical information.
The Wall Street Journal also offers historical bond rates, which differ from the government's information in an important respect. The Fed and Treasury show coupon rates, while the Wall Street Journal displays the current yield. For bonds, the coupon rate is the percentage interest rate paid to bondholders, while the current yield is the interest payment divided by the current market price of the bond, explains Investopedia.