Subject: Re: OT: T-bills
For a US resident:

Tax treatment of Treasury bills (T-bills):
Federal tax: Income earned from T-bills is taxed federally by the Internal Revenue Service.
State tax: T-bill income is not subject to state tax.
Local tax: T-bill income is not subject to local income taxes.
Overall: T-bill income is partially but not entirely tax-exempt.

T-bills can have an advantage over money market funds, depending on where you live, etc.