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Using the nine-year radio-pulsar timing data set from the North AmericanNanohertz Observatory for Gravitational Waves (NANOGrav), collected at AreciboObservatory and the Green Bank Telescope, we have measured the positions,proper motions, and parallaxes for 37 millisecond pulsars. We report twelvesignificant parallax measurements and distance measurements, and eighteen lowerlimits on distance. We compare these measurements to distances predicted by theNE2001 interstellar electron density model and find them to be in generalagreement. We use measured orbital-decay rates and spin-down rates to confirmtwo of the parallax distances and to place distance upper limits on othersources; these distance limits agree with the parallax distances with oneexception, PSR J1024-0719, which we discuss at length. Using the proper motionsof the 37 NANOGrav pulsars in combination with other published measurements, wecalculate the velocity dispersion of the millisecond pulsar population inGalactocentric coordinates. We find the radial, azimuthal, and perpendiculardispersions to be 46, 40, and 24 km s-1, respectively, in a model that allowsfor high-velocity outliers; or 81, 58, and 62 km s-1 for the full population.These velocity dispersions are far smaller than those of the canonical pulsarpopulation, and are similar to older Galactic disk populations. This suggeststhat millisecond pulsar velocities are largely attributable to their being anold population rather than being artifacts of their birth and evolution asneutron star binary systems. The components of these velocity dispersionsfollow similar proportions to other Galactic populations, suggesting that ourresults are not biased by selection effects.

The NANOGrav Nine-year Data Set: Astrometric Measurements of 37 Millisecond Pulsars