| Duncan to Silver Firs (Washington) | 1,549.10 mi (2,493.03 km) |
| Duncan to Silver Spring (Maryland) | 1,194.15 mi (1,921.79 km) |
| Duncan to Silver Springs Shores (Florida) | 1,004.82 mi (1,617.10 km) |
| Duncan to Silverdale (Washington) | 1,564.98 mi (2,518.59 km) |
| Duncan to Silverton (Oregon) | 1,496.37 mi (2,408.17 km) |
| Duncan to Simi Valley (California) | 1,185.37 mi (1,907.66 km) |
| Duncan to Simpsonville (South Carolina) | 889.72 mi (1,431.86 km) |
| Duncan to Sioux City (Iowa) | 555.81 mi (894.50 km) |
| Duncan to Sioux Falls (South Dakota) | 625.01 mi (1,005.86 km) |
| Duncan to Skokie (Illinois) | 755.98 mi (1,216.63 km) |
| Duncan to Sleepy Hollow (New York) | 1,383.17 mi (2,226.00 km) |
| Duncan to Slidell (Louisiana) | 557.97 mi (897.96 km) |
| Duncan to Smithfield (North Carolina) | 1,107.59 mi (1,782.49 km) |
| Duncan to Smithfield (Utah) | 906.06 mi (1,458.16 km) |
| Duncan to Smithville (Missouri) | 382.65 mi (615.82 km) |
