40 ILCS 5/2-105
"Member": Members of the General Assembly of this State including persons who enter military service while a member of the General Assembly and any person serving as Governor, Lieutenant Governor, Secretary of State, Treasurer, Comptroller, or Attorney General for the period of service in such office.
Any person who has served for 10 or more years as Clerk or Assistant Clerk of the House of Representatives, Secretary or Assistant Secretary of the Senate, or any combination thereof, may elect to become a member of this system while thenceforth engaged in such service by filing a written election with the board. Any person so electing shall be deemed an active member of the General Assembly for the purpose of validating and transferring any service credits earned under any of the funds and systems established under Articles 3 through 18 of this Code.
40 ILCS 5/2-105