The following PDF contains graphs of the demographic breakdown of the 1206 released subjects from whom we collected behavioral data as part of the HCP Young Adult (HCP-YA) Study:
Note: For HCP-YA, subjects were recruited as families (a twin pair and their siblings) in order to facilitate studies of heritability of brain structure and function. Many of the demographic measures collected could be identifying (especially in combination) in a family study such as HCP-YA. Therefore, if you require demographic and family structure details on the subject level, you will need to apply for restricted data access using this form: https://humanconnectome.org/storage/app/media/data_use_terms/DataUseTerms_HCP_RestrictedAccess_30Nov2017.pdf