Triangular Jog

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Historical Marker #1850 in Simpson County notes the irregular boundary protrusion that occurs on the Kentucky-Tennessee state line where Interstate 65 crosses the border.

Looking at almost any map of the United States, it is easy to see the unusual boundaries between some to the states. Some state lines are determined by geographical features, such as Kentucky’s northern border of the Ohio River. Other boundaries are surveyed and appear quite uniform until upon closer examination some irregularities are found.

One such irregularity is located on Kentucky’s southern border where Simpson County dips triangularly southward into Robertson and Sumner Counties in Tennessee. This abnormal offset occurred when surveyors, who were using imperfect astronomy measurements in 1780, were not able to keep a straight bearing due to weather conditions. In addition, it is believed that their calculations were further altered due to the large deposits of iron ore, which threw off their surveying compass readings.

The irregular boundary was kept intact until a dispute arose and the line was resurveyed in the 1830s. It became obvious that if the original line was moved it would cause difficult issues of state citizenship with those that lived in the area in contention. Another survey was made in 1859 that determined that about 100 acres of property of a Sumner County, Tennessee, citizen named Middleton was actually in Kentucky. The surveyors determined that this man’s property should remain in Tennessee. So, within the triangular offset, a rectangular offset was created that protruded northeastward.

Today, with modern technology tools such as Global Positioning Systems the “Simpson County Offset” would not occur, but working with the equipment that eighteenth century surveyors did, it is surprising that many more such errors did not happen.