The 4-H youth development organization operates county and municipal chapters, and is affiliated with Cooperative Extension Services around the country. Each state oversees the 4-H clubs in their boundaries differently, and each chapter must make their own arrangements for tax exemption. This means that many chapters are tax exempt, so you can donate to them and claim a deduction, but as of 2011, not all chapters are.
4-H chapters that have obtained a 501(c)3 status are considered charities, and donations to these 4-H programs are indeed tax deductible. Some of the many 4-H chapters that have a 501(c)3 include those in Gainesville, Texas; Baton Rouge, Louisiana; Salt Lake City, Utah; Tucson, Arizona; Little Rock, Arkansas and Essex County, Massachusetts. The Internal Revenue Service maintains a searchable database of charities that have 501(c)3 certification, called Publication 78. You can check local chapters on that database.
Chapters must follow protocol to get a 501(c)3, so whether the donation is tax exempt depends on whether your chapter has complied. First, they must get an official 4-H name and emblem charter from the Director of Extension and the State 4-H Office where they're located, then they must get a federal EIN or employer identification number. After this, the State 4-H office sends a list of all complying groups in the state to the National 4-H office, and all of these chapters receive tax exempt status. As of 2010, the 4-H organization still has some chapters that need to comply.
If you want to give money to your local 4-H chapter because you support the cause, you should do so, no matter what its tax exempt status. If you are giving to a 501(c)3-certified chapter, get a receipt for the amount of your donation. You can deduct your donation as a charitable contribution on your IRS Form 1040.
As of 2010, the National 4-H is actively pushing for chapters to obtain their status, either as an independent 501(c)3 or as a subordinate organization of another group. They provide assistance to municipal and county groups through the State 4-H chapters. Thus it is not unreasonable to think that 4-H chapters in the future will all be 501(c) 3 certified, for a tax exemption.