  We report the combined results of eight searches for strong gravitational
lens systems in the full 5,000 sq. deg. of Dark Energy Survey (DES)
observations. The observations accumulated by the end of the third observing
season fully covered the DES footprint in 5 filters (grizY), with an $i-$band
limiting magnitude (at $10\sigma$) of 23.44. In four searches, a list of
potential candidates was identified using a color and magnitude selection from
the object catalogs created from the first three observing seasons. Three other
searches were conducted at the locations of previously identified galaxy
clusters. Cutout images of potential candidates were then visually scanned
using an object viewer. An additional set of candidates came from a
data-quality check of a subset of the color-coadd "tiles" created from the full
DES six-season data set. A short list of the most promising strong lens
candidates was then numerically ranked according to whether or not we judged
them to be bona fide strong gravitational lens systems. These searches
discovered a diverse set of 247 strong lens candidate systems, of which 81 are
identified for the first time. We provide the coordinates, magnitudes, and
photometric properties of the lens and source objects, and an estimate of the
Einstein radius for 81 new systems and 166 previously reported. This catalog
will be of use for selecting interesting systems for detailed follow-up,
studies of galaxy cluster and group mass profiles, as well as a
training/validation set for automated strong lens searches.
