The ''Climatology of Brookhaven National Laboratory 1974 to 1977'' is a supplement to BNL 50466, ''Climatology of Brookhaven National Laboratory 1949 to 1973'' which was prepared from data collected by the Brookhaven Meteorology Group formed in August 1948. This publication updates some meteorological summaries and includes analyses of humidity and solar radiation data not included in the original climatological report. Results are presented in tabular form to facilitate usage. Data are given in the form of frequency distributions, percentage frequency distributions, extremes, ranges, and averages as being most adaptable for further research.