Again, it's going to depend on the laws of each state, which vary. Each of those states may allow a board to be only a single individual. However, the laws may also require that the same person cannot be President and Secretary (for example).
In Delaware, the same person could be member, director and officer.
In Washington, the same person cannot be President and Secretary.
In Virginia, the same person can hold all those positions.
In Maryland, the same person cannot be both president and vice-president (although only the offices of president, secretary and treasurer are required.
In Iowa, the same person may hold all those positions.
The IRS doesn't have laws that pertain to members, officers and directors of a nonprofit corporation. Those matters are controlled by state law. However, for some charitable organizations that are tax exempt, certain decisions must be removed from the members to maintain tax-exempt status. That really is a completely separate matter that is quite complicated and cannot be answered without a specific corporation in mind.