According to theU.S. Census Bureau, the county has a total area of 488 square miles (1,260 km2), of which 479 square miles (1,240 km2) is land and 8.9 square miles (23 km2) (1.8%) is water.[5]
Most of the western portion of Tattnall County, defined by a line running fromCobbtown south toCollins, then east to a point halfway toBellville, and then south and southwest to the middle of the county's southern border, is located in theOhoopee River sub-basin of theAltamaha River basin. The northeastern portion of the county, from Cobbtown to east ofReidsville, is located in theCanoochee River sub-basin of theOgeechee River basin. The southeastern and southwestern parts of Tattnall County are located in the Altamaha River sub-basin of the larger river basin by the same name.[6]
TheGeorgia Department of Corrections operates theRogers State Prison, and formerly theGeorgia State Prison inunincorporated Tattnall County,[18] nearReidsville.[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. The prison cemetery has 971 burials which are inmates who died while serving time from 1937 to present.
Another large government parcel of land is the 10,000 acre Big Hammock Wildlife Management Preserve in the southwest section of the county. The entrance is 12 miles south of Glennville on Hwy 144 at the Ohoopee River Bridge. This is controlled by the GA Department of Natural Resources under the Wildlife Resources Division. It has a shooting range and 2 boat ramps along the river which are north of the merger with the Altamaha River which forms the southern border of the county. Permits are issued for seasonal hunting of deer, turkey, and small game. Updates are posted at www.GoHuntGeorgia.com
Another large government land parcel is on the eastern side of Tattnall County along the border with Evans, Liberty, and Long Counties. This 6000+ acres forms the western side of the Fort Stewart Army Reservation which is based in Hinesville, GA. Originally this was farmland purchased by the Army during and after World War II. It has since been turned into forest land with no development. The current Ft. Stewart Land Use Development plan excludes any of this property in their 25-year future planning approved by the Department of Defense. This land mass can be viewed on Google Maps with additional info from the website for the Ft. Stewart Joint Land Use Study. (www.mrrpc.com/Misc_pdfs/Fort_Stewart_JLUS_Final_Report.pdf)