The Bogleheads' Guide to Investing

Even though EE and I Savings Bonds are purchased with after-tax money for your taxable account, they are tax-deferred for up to 30 years. This makes Savings Bonds an ideal candidate for your portfolio when you need to hold bonds in your taxable account, but don’t need current income from your bond holdings. Like other Treasury issues, Savings Bonds are free from state and local taxes.