'Harrow' comes from Old English hearg, a heathen temple.
The temple was probably on the hill, where St Mary's Church now stands. The station opened in 1880 as Harrow and became Harrow-on-the-Hill in 1894, though it sits at the foot of the hill, in what was then the hamlet of Greenhill, recorded as Grenehulle in 1334. Greenhill has since grown into Harrow's town centre.