Miss. Code § 3-3-5
The counties lying immediately on the Mississippi River shall, respectively, have and possess jurisdiction and extend to the western boundary of the state, within the space embraced, by extending their boundary lines which strike the river, on a continuous direct course to the extreme boundary of the state, including all islands that may be within the limits just defined; and the counties bordering on the Gulf of Mexico, to wit: Jackson, Harrison and Hancock, shall, respectively, have and possess jurisdiction and extend to the southern boundary of the state within the space embraced by extending their boundary lines which strike the Gulf of Mexico, or the inlets thereto, on a continuous direct course to the southern boundary of the state, including all islands that may lie within the limits thus defined.
Miss. Code § 3-3-5