National Council of Nonprofit Associations (NCNA)

The National Council of Nonprofit Associations (NCNA) is the network of state and regional nonprofit associations serving over 25,000 members in 41 states and the District of Columbia. NCNA links local organizations to a national audience through state associations and helps small and midsize nonprofits: manage and lead more effectively; collaborate and exchange solutions; engage in critical policy issues affecting the sector; and achieve greater impact in their communities.
Association of Fundraising Professionals (AFP)

Through education, training, and advocacy the AFP enables people and organizations to practice effective and ethical fundraising. There are many regional chapters in Illinois including Champaign, Peoria, and the Capital Area Chapter in Springfield that encompasses the area of Jacksonville to Decatur.
The Independent Sector

A publisher of many important publications including the annual survey Giving & Volunteering that can be found at this site. Also contains legal and legislative information.