We report on a mid-infrared Q-switched erbium-doped all-fiber laser using a dysprosium-doped silica fiber as saturable absorber for the first time in this wavelength range. Moreover, we demonstrate the use of a highly reflective chirped fiber Bragg grating written in a silica fiber as the input coupler for such lasers. This Q-switched all-fiber laser generates a stable pulse train centered at 2798 nm with a maximum average power of 670 mW at a repetition rate of 140 kHz with a pulse duration of 240 ns and a pulse energy of 4.9 µJ.