  The Quintuplet star cluster is one of only three known young ($<10$ Myr)
massive (M $>10^4$ M$_\odot$) clusters within $\sim100$ pc of the Galactic
Center. In order to explore star cluster formation and evolution in this
extreme environment, we analyze the Quintuplet's dynamical structure. Using the
HST WFC3-IR instrument, we take astrometric and photometric observations of the
Quintuplet covering a $120''\times120''$ field-of-view, which is $19$ times
larger than those of previous proper motion studies of the Quintuplet. We
generate a catalog of the Quintuplet region with multi-band, near-infrared
photometry, proper motions, and cluster membership probabilities for $10,543$
stars. We present the radial density profile of $715$ candidate Quintuplet
cluster members with $M\gtrsim4.7$ M$_\odot$ out to $3.2$ pc from the cluster
center. A $3\sigma$ lower limit of $3$ pc is placed on the tidal radius,
indicating the lack of a tidal truncation within this radius range. Only weak
evidence for mass segregation is found, in contrast to the strong mass
segregation found in the Arches cluster, a second and slightly younger massive
cluster near the Galactic Center. It is possible that tidal stripping hampers a
mass segregation signature, though we find no evidence of spatial asymmetry.
Assuming that the Arches and Quintuplet formed with comparable extent, our
measurement of the Quintuplet's comparatively large core radius of
$0.62^{+0.10}_{-0.10}$ pc provides strong empirical evidence that young massive
clusters in the Galactic Center dissolve on a several Myr timescale.
