The project combines two sources of information. The word counts themselves come from the HathiTrust Research Center (HTRC), which has tabulated them at the page level in 4.8 million public-domain volumes. Information about genre comes from a parallel project led by Ted Underwood, and supported by the National Endowment for the Humanities and the American Council of Learned Societies.
The dataset genres.json contains (sub)genre classifications for novels published between 1770 and 1915. The genres covered are
gothic novels
"silver fork" novels
national tale novels