We present deep and accurate optical photometry of the Local Group starburst galaxy IC 10. The photometry is based on two sets of images collected with the Advanced Camera for Surveys and with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We provide new estimates of the tip of the red giant branch TRGB) magnitude, m(F814W)(TRGB) = 21.90 +/- 0.03, and of the reddening, E(B - V) = 0.78 +/- 0.06, using field stars in the Small Magellanic Cloud (SMC) as a reference. Adopting the SMC and two globulars, omega Cen and 47 Tuc, as references we estimate the distance modulus to IC 10: independent calibrations give weighted average distances of mu = 24.51 +/- 0.08 (TRGB) and mu = 24.56 +/- 0.08 (RR Lyrae). We also provide a new theoretical calibration for the TRGB luminosity, and using these predictions we find a very similar distance to IC 10 (mu approximate to 24.60 +/- 0.15). These results suggest that IC 10 is a likely member of the M31 subgroup.