Widely-tunable cw laser action has been demonstrated in a diode-pumped Yb:KYF(4) crystal. A comprehensive characterization of the active material and laser performance are reported, with particular attention to single-frequency laser operation. Single longitudinal-mode operation is achieved in the tuning range from 1020 to 1045 nm with a maximum output power of 150 mW. The relative intensity noise of the single-frequency laser is limited by quantum noise contribution for Fourier frequencies larger than 1 MHz.