One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at , corresponding to an excited state in 23O at , as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d-wave neutron knockout, providing support for a assignment of . The associated spectroscopic factor was deduced to be by comparing the measured cross section () with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron orbital is in line with the shell closure in 24O.