Many nonprofits acquire their statistics from the government agencies listed above. The value of nonprofit reports is that they usually present those statistics in easy-to-read reports that are more accessible than the raw data offered by government agencies. Nonprofits also use data to argue particular points or issues, which, depending on your own research, may be of greater value to you than raw data.
The Sentencing Project: Incarcerated Women & Girls
Prison Policy Initiative: California profile
California Coalition for Women Prisoners