We present high-precision timing data over timespans of up to 11 years for 45millisecond pulsars observed as part of the North American NanohertzObservatory for Gravitational Waves (NANOGrav) project, aimed at detecting andcharacterizing low-frequency gravitational waves. The pulsars were observedwith the Arecibo Observatory and/or the Green Bank Telescope at frequenciesranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximatelymonthly cadence, with six high--timing-precision pulsars observed weekly, andall were observed at widely separated frequencies at each observing epoch inorder to fit for time-variable dispersion delays. We describe our methods fordata processing, time-of-arrival (TOA) calculation, and the implementation of anew, automated method for removing outlier TOAs. We fit a timing model for eachpulsar which includes spin, astrometric, and, if necessary, binary parameters,in addition to time-variable dispersion delays and parameters that quantifypulse-profile evolution with frequency. The new timing solutions provide threenew parallax measurements, two new Shapiro-delay measurements, and two newmeasurements of large orbital-period variations. We fit models thatcharacterize sources of noise for each pulsar. We find that 11 pulsars showsignificant red noise, with generally smaller spectral indices than typicallymeasured for non-recycled pulsars, possibly suggesting a different origin.Future papers will use these data to constrain or detect the signatures ofgravitational-wave signals.
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