  Multiply gravitationally lensed objects with known time delays can lead to
direct determinations of H$_0$ independent of the distance ladder if the mass
distribution of the lens is known. Currently, the double QSO 0957+561 is the
only lensed object with a precisely known time delay. The largest remaining
source of systematic error in the H$_0$ determination results from uncertainty
in the mass distribution of the lens which is comprised of a massive galaxy
(G1) and the cluster in which it resides.
  We have obtained V-band CCD images from CFHT in order to measure the mass
distribution in the cluster from its gravitional distorting effect on the
appearance of background galaxes. We use this data to constuct a
two-dimensional mass map of the field. A mass peak is detected at the
$4.5\sigma$ level, offset from, but consistent with, the position of G1. Simple
tests reveal no significant substructure and the mass distribution is
consistent with a spherical cluster. The peak in the number density map of
bright galaxies is offset from G1 similarly to the mass peak.
  We constructed an azimuthally averaged mass profile centered on G1 out to 2
\arcmin ($400 h^{-1}$ kpc). It is consistent with an isothermal mass
distribution with a small core ($r_c \approx 5 \arcsec = 17 h^{-1}$ kpc). The
inferred mass within 1 Mpc is consistent with the dynamical mass estimate but
$2\sigma$ higher than the upper limits from a ROSAT X-ray study.
  We discuss implications for H$_0$ in a future paper.
