Three classification systems (taxonomies) of not-for-profits
I. IRS Sub-Sections
II. NTEE Broad Categories and Major Groups
The National Center for Charitable Statistics web site describes the National Taxonomy of Exempt Entities or NTEE, a classification for nonprofit organizations recognized as tax exempt under the Internal Revenue Code.
Here is an introduction to the concept of NTEE classification, listing the 10 "broad categories" that make up this classification, and the 26 "major groups" that fall within these categories. For a summary listing of all codes, visit the NTEE-CC Two Pager. For a complete manual with in-depth description, examine the NTEE-CC Manual.
III. NAICS Industry Codes
The National Center for Charitable Statistics web site is a great place to gather current statistics on total numbers of organizations by category. See especially the section: Data Analysis Tools > "Table Wizard." Note the distinction made between private foundations and public charities.
A wealth of statistics can also be found in the Nonprofit Almanac 2016, available by library subscription. Selected data has been updated in the freely available 2015 Nonprofit Sector in Brief almanac.
Perhaps the single best directory of U.S. nonprofits on the web, GuideStar (http://www.guidestar.org/) (password access only) offers basic directory information plus financial statements, mission and programs, goals and results, and leaders.
For private foundations specifically, Guidestar can be used, but the The Foundation Directory, available on level A of the library, in Graduate Reference 061 F771d, is also useful.
For foreign nonprofits, consult idealist.org. This directory is open access.
Run a Google search on your organization as well, for news about the organization and the organizational home page.
For mention in newspapers, magazine, or trade publication, visit the library subscription database LexisNexis Academic, or Business Source Complete .
For nonprofits in the Lehigh Valley, visit the library subscription database Morning Call via Proquest.