Which officer keeps the "Great Seal" of Illinois?

The correct answer is the Secretary of State, who is responsible for keeping the "Great Seal" of Illinois. The Great Seal serves as an important symbol of the state, used to authenticate official documents and acts of the government. The Secretary of State's office is tasked with maintaining state records and ensuring the proper use of the seal, aligning with its role in overseeing many administrative functions of the state government.

The other options, while significant positions within Illinois government, do not hold this specific responsibility. The Governor, Attorney General, and State Comptroller each have their own distinct roles that do not include the custody of the state's Great Seal, which is specifically designated to the Secretary of State's office.