The answer depends on where your nonprofit is located. In Arizona, you only need one board member to form a nonprofit corporation. In other states, you may need more. For example, in Washington, nonprofits must have at three directors if it has applied for tax-exempt status with the IRS.
While state law governs the minimum number of directors, those nonprofits that wish to become tax-exempt should strive to recruit at least three independent directors. Doing so shows the IRS and potential donors that the organization is not overly influenced by any single person and that business decisions are made in the best interests of the nonprofit and the communities it serves.