Shared from our friends at the National Council of Nonprofits:

Are you looking for data sources on the nonprofit sector but not sure where to start? This Library of Congress research guide offers a comprehensive roadmap for understanding the nonprofit landscape in the United States. It provides curated links to essential data sources, including IRS Form 990 filings, grantmaking directories, and professional associations. The guide is meant to help nonprofit staff and researchers effectively navigate the legal, financial, and organizational complexities of the charitable sector.