Constitution of the State of Georgia
Article IX Counties & Municipal Corporations
Section III Intergovernmental Relations
Paragraph I: Intergovernmental contracts.

The state, or any institution, department, or other agency thereof, and any county, municipality, school district, or other political subdivision of the state may contract for any period not exceeding 50 years with each other or with any other public agency, public corporation, or public authority for joint services, for the provision of services, or for the joint or separate use of facilities or equipment; but such contracts must deal with activities, services, or facilities which the contracting parties are authorized by law to undertake or provide. By way of specific instance and not limitation, a mutual undertaking by a local government entity to borrow and an undertaking by the state or a state authority to lend funds from and to one another for water or sewerage facilities or systems or for regional or multijurisdictional solid waste recycling or solid waste facilities or systems pursuant to law shall be a provision for services and an activity within the meaning of this paragraph.

Georgia Code
Title 36 Local Government
Provisions Applicable to Counties and Municipal Corporations
Chapter 69A Interlocal Cooperation
36-69A-4. Joint exercise of powers, privileges, or authority; agreements with public agencies of other states; required information and provisions; limitations on contracts

(a) Any power or powers, privileges, or authority exercised or capable of exercise by a public agency of this state may be exercised and enjoyed jointly with any other public agency of any other state or of the United States to the extent that laws of such other state or of the United States permit such joint exercise or enjoyment. The authority for joint or cooperative action of political subdivisions shall apply to powers, privileges, or authority vested in, funded by, or under the control of their governing bodies. 

(b) Any public agency in this state may enter into agreements with a public agency in another state for joint or cooperative action pursuant to the provisions of this chapter to effectuate the purposes of this chapter. Appropriate action of the governing bodies of the participating public agencies by resolution or otherwise pursuant to law shall be necessary before any such agreement may enter into force. Any such agreement shall be subject to the requirements provided by the Constitution and general laws of this state with respect to intergovernmental contracts.