We present a very large extension of the Galactic plane CO survey of Dame+ (2001ApJ...547..792D) to the entire northern sky ({delta}>-17{deg}). The extension was carried out with the same telescope as was used for the plane survey, the CfA 1.2m, and perfectly meshes with its irregular boundaries in latitude. A total of 382,202 CO(1-0) spectra uniformly sample the high-latitude sky with a true-angle spacing of 0.25{deg} or better. The final reduced and folded spectra have a uniform sensitivity of 0.18K in 0.65km/s channels and provide a velocity coverage of +/-47.1km/s. We describe the observational techniques and the data reduction and provide various summary maps of the spatial and velocity distributions of CO emission over the northern sky, and a catalog of the molecular clouds we found there. We also describe the CO spectral line data cubes that we have made available online.