Extensive information regarding past and present interest rates is available on the U.S. Department of the Treasury website. It is in the Resource Center, under the Data and Charts Center, and in the category of Interest Rate Statistics.
The first chart to load when clicking on Daily Treasury Yield Curve Rates shows the current day's yield rates for loans ranging from only a month to 30 years. However, there is also a dropdown menu that allows users to select any time period starting from 1990 and extending to the current day. The site also offers categories and charts labeled Daily Treasury Bill Rates, Daily Treasury Long-Term Rates, Daily Treasury Real Yield Curve Rates, Daily Treasury Real Long-Term Rates, Historic Treasury Rates Chart and Historic Yield Curve Chart.