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49.30 miles ; from I-85 near LaGrange to Columbus. Opened in late 1970s.
David Sturm writes:
"[I-185] used to continue south from the 27/280 intersection 'secretly' into Fort Benning, although now Rand McNally shows it. What no one shows is that after it merges heading west with First Division Road, stay on it a couple miles, and turn left onto Dixie Road following the TO AL 165 signs, and you discover a 'secret BRIDGE' over the Chattahoochee. It takes you directly to Ft Mitchell AL and an intersection with AL 165. Folks from the area of AL I lived in would go from Dothan to Atlanta via this route: US 431 to Lakepoint Park, AL 165 to the secret bridge, across Ft Benning to I-185. Very efficient route, unless Ft Benning is on alert. :)"
I-185 (proposed number rejected) North Carolina
This was a 24-mile route submitted by the state to AASHTO in 2003. Interstate 185 would be applied "Beginning at the intersection of Interstate Route 85 and Interstate Route 85 Business in Lexington, then northwesterly over I-85 Business for 4 miles to the intersection of U.S. Route 52, then northwesterly and northerly over U.S. Route 52 for 20 miles to the intersection of Interstate Route 40 in Winston-Salem." 
Basically, this would have applied the I-185 number to US 52 between I-85 and I-40. Some would argue that since I-185 would have connect two interstates, it should have started with an even number (see explanation).
It's all academic now; on May 30, 2003, AASHTO rejected the proposal, saying the acro(FWHA) has not designated the route as a part or future part of the Interstate system.  However, the state is planning to submit an I-285 proposal along nearly the same route.
I-185 South Carolina
17.70 miles ; from I-385 west toward I-85, then north toward Greenville. Co-signed with US 29 for its entire length. Originally, Interstate 185 was 2.98 miles long and existed north of I-85 only. This segment was built between 1962 and 1965.
A toll bypass called the "Southern Connector" opened Feb. 27, 2001, connecting I-85 at I-185 to I-385 at US 276.  The I-185 designation was extended over this 14-mile road, after AASHTO approved the "future I-185" designation in its December 2000 meeting. 
The highway offers interchanges at SC 20, US 25, and Fork Shoals Road.  Although the road is fully open, SCDOT still needs to update mileposts and add guide signs.