Lincoln County is bounded on the south by Madison and Limestone Counties Alabama; on the west by Giles County; on the northwest by Marshall County; on the north by Bedford County; on the northeast by Moore County; and on the east by Franklin County.

County Boundary Changes:

Between 1810-1820, a small portion of Indian land was added forming the southeast corner of the county. In 1836, the northwest portion of Lincoln County given to form part of Marshall County. In 1871, the northeast portion of Lincoln County given to form over one half of Moore County.

Topography

 Lincoln County lies almost wholly within the central basin of Middle Tennessee. The geological situation of the county is about equally divided between the siliceous group of the lower Carboniferous formation, and the Nashville group of the Silurian formation. On the line of the railroad may be seen large quantities of black shale, which is so impregnated with petroleum of bitumen that it will sustain for a month a fire when kindled on it. This black shale is also rich in sulpheret of iron, by the decomposition of which copperas and alum are formed. It easily disintegrates upon exposure and is valueless except for the manufacture of the salts mentioned. Many of the limestone rocks are but aggregations of fossil remains.

A few miles east of Fayetteville is a quarry where a very fair article of reddish variegated marble is found. This marble is sometimes injured by particles of iron pyrites. The county is divided into two almost equal parts by the Elk River, which with its numerous tributaries affords it excellent water facilities. The streams which enter this river from the north are Bradshaw Creek, Swan Creek, Cane Creek, Norris Creek, Mulberry Creek, Roundtree Creek, Tucker Creek and Farris Creek. Those from the south are Shelton Creek, Duke Creek, Stewart Creek, Wells Creek, Coldwater Creek, and Kelley Creek.

Between Elk River and the Alabama line is a belt of high land which is the watershed between Elk River and the Tennessee River. This watershed embraces a strip about eight miles wide and includes nearly one-third of the county. It is an exceedingly level high plateau and is not well drained. The sub-soil is a pale yellowish clay porous and leachy except in swamps where the clay is bluish. However, a few spots are found with a good red clay subsoil, and when this is found, lands are rated highter. No limestone is seen on this plateau and the main vegetation is wild growth.

The remainder of the county comprises spacious valleys, alternating with productive hills and ridges. Upon some of the hills however, the loose limestone lies in such abundance as to preclude cultivation. The valleys of Elk River and Cane Creek will average a mile in width, and the latter is probably fifteen miles long. The land in these two valleys is as productive as any in the State. Many knolls near Elk River are upraised alluvium. An abundance and a general variety of timber grows in the county. It is mainly of the following varieties: Linn, buckeye, hickory, poplar, box elder, black walnut, wild cherry, black locust, chestnut, beech, gum, dogwood, ironwood, horn beam, sugar tree, hackberry, cedar and elm.
(Goodspeed, 767)