I think this is the Theodore Duncan listed in 1860 census in Platte Twsp, Clay County, Post office Missouri City. Family #1405. Accordingly listed as 32 years old native of Kentucky. He is next door to a James Duncan also of Kentucky age 43. Both are fairly well off but Theodore the more of the 2 with a property value listed at 11,000$. (read likely slave owner)

I'll keep looking.

FWIW
John R.