[5] Most of the western portion of Tattnall County, defined by a line running from Cobbtown south to Collins, then east to a point halfway to Bellville, and then south and southwest to the middle of the county's southern border, is located in the Ohoopee River sub-basin of the Altamaha River basin.

[19] As of 2020, according to the Georgia State Prison Fact Sheet, the facility occupies 9,800 acres of land inside Tattnall County and provides 162 staff housing units on the reservation.

Another large government parcel of land is the 10,000 acre Big Hammock Wildlife Management Preserve in the southwest section of the county.

This 6000+ acres forms the western side of the Fort Stewart Army Reservation which is based in Hinesville, GA.

Fort Stewart has the Department of Defense Education Activity (DoDEA) as its local school district,[21] for the elementary level.