A galaxy group catalog is built from the sample of the 2MASS Redshift Survey almost complete to K_s_=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^M_{sun}_. Group masses inferred from K_s_ 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 3000 and 10000km/s. The 24044 galaxies in this range are identified with 13607 entities, 3461 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 6h^-1^x10^12^M_{sun}_ but the count normalization is poor. Summing all the mass associated with the galaxy groups between 3000 and 10000km/s gives a density of collapsed matter as a fraction of the critical density of {Omega}_collapsed_=0.16.