Nonprofit organizations with 501(c)(3) status are required to file Form 990, Return of Organizations Exempt from Income Tax, with the IRS. The form includes financial statements and background information on the nonprofit, including salaries of key employees (i.e. director, head, officers).
Form 990 is not as detailed as 10K reports that publicly traded companies are required to file, however, they still contain useful information.
A searchable database of more than 620,000 nonprofit organizations in the United States. Registration required to verify a nonprofit's legitimacy, learn whether a contribution will be tax deductible, or view a nonprofit's recent Forms 990.