Partial oxidation of methanol to formaldehyde over Cu(110) is one of the most studied catalytic reactions in surface science, yet the local site of the reaction intermediate, methoxy, remains unknown. Using a combination of experimental scanned-energy mode photoelectron diffraction, and density functional theory, a consistent structural solution is presented in which all methoxy species occupy twofold coordinated "short-bridge" adsorption sites. The results are consistent with previously-published scanning tunnelling microscopy images and theoretical calculations of the reaction mechanism.