Its position as located in a 1918 survey is located at 39 50 N 98 35 W / 39.833 N 98.583 W / 39.833;-98.583 (Geographic Center of the Contiguous United States), about 2.6 miles (4.2 km) northwest of the center of Lebanon, Kansas, approximately 12 miles (19 km) south of the Kansas-Nebraska border.

Based on this passage, city in the middle of the united states? Let's give stream of consciousness first:
The relevant information to answer the above question is: Its position as located in a 1918 survey is located at 39 50 N 98 35 W / 39.833 N 98.583 W / 39.833;-98.583 (Geographic Center of the Contiguous United States), about 2.6 miles (4.2 km) northwest of the center of Lebanon, Kansas, approximately 12 miles (19 km) south of the Kansas-Nebraska border.
So, the final answer is Lebanon , Kansas.