Recent modeling of hydrogen-rich Type II supernova ( SN II ) light curves suggests the presence of dense circumstellar material ( CSM ) surrounding the exploding progenitor stars . This has important implications for the activity and structure of massive stars near the end of their lives . Since previous work focused on just a few events , here we expand to a larger sample of twenty well-observed SNe II . For each event we are able to constrain the progenitor zero-age main-sequence ( ZAMS ) mass , explosion energy , and the mass and radial extent of dense CSM . We then study the distribution of each of these properties across the full sample of SNe . The inferred ZAMS masses are found to be largely consistent with a Salpeter distribution with minimum and maximum masses of 10.4 and 22.9 M _ { \odot } , respectively . We also compare the individual ZAMS masses we measure with specific SNe II that have pre-explosion imaging to check their consistency . Our masses are generally comparable to or larger than the pre-explosion imaging masses , potentially helping ease the red supergiant problem . The explosion energies vary from ( 0.1 - 1.3 ) \times 10 ^ { 51 } { erg } , and for \sim 70 \% of the SNe we obtain CSM masses in the range between 0.18 - 0.83 M _ { \odot } . We see a potential correlation between the CSM mass and explosion energy , which suggests that pre-explosion activity has a strong impact on the structure of the star . This may be important to take into account in future studies of the ability of the neutrino mechanism to explode stars . We also see a possible correlation between the CSM ’ s radial extent and ZAMS mass , which could be related to the time with respect to explosion when the CSM is first generated .