We study the coherence and density modulation of a non-equilibrium exciton-polariton condensate in a one-dimensional valley with disorder. By means of interferometric measurements we evidence a modulation of the first-order coherence function and we relate it to a disorder-induced modulation of the condensate density, that increases as the pump power is increased. The non-monotonous spatial coherence function is found to be the result of the strong non-equilibrium character of the one-dimensional system, in the presence of disorder.