  De-excitation $\gamma$ cascades from neutron captures form a dominant
background to MeV-scale signals. The Geant4 Monte Carlo simulation toolkit is
widely used to model backgrounds in nuclear and particle physics experiments.
While its current modules for simulating (n, $\gamma$) signals, GFNDL and
G4PhotoEvaporation, are excellent for many applications, they do not reproduce
known gamma-ray lines and correlations relevant at 2-15 MeV. G4CASCADE is a new
data-driven Geant4 module that simulates (n, $\gamma$) de-excitation pathways,
with options for how to handle shortcomings in nuclear data. Benchmark
comparisons to measured gamma-ray lines and level structures in the ENSDF
database show significant improvements, with decreased residuals and full
energy conservation. This manuscript describes the underlying calculations
performed by G4CASCADE, its various usage options, and benchmark comparisons.
G4CASCADE for Geant4-10 is available on GitHub at
https://github.com/UCRDarkMatter/CASCADE
