  A galaxy group catalog is built from the sample of the 2MASS Redshift Survey
almost complete to Ks=11.75 over 91% of the sky. Constraints in the
construction of the groups were provided by scaling relations determined by
close examination of well defined groups with masses between 10^11 and 10^15
Msun. Group masses inferred from Ks luminosities are statistically in agreement
with masses calculated from application of the virial theorem. While groups
have been identified over the full redshift range of the sample, the properties
of the nearest and farthest groups are uncertain and subsequent analysis has
only considered groups with velocities between 3,000 and 10,000 km/s. The
24,044 galaxies in this range are identified with 13,607 entities, 3,461 of
them with two or more members. A group mass function is constructed. The
Sheth-Tormen formalism provides a good fit to the shape of the mass function
for group masses above 6/h x 10^12 Msun but the count normalization is poor.
Summing all the mass associated with the galaxy groups between 3,000 and 10,000
km/s gives a density of collapsed matter as a fraction of the critical density
of Omega_collapsed = 0.16.
