In the whole US, the 1860 census showed a William Feldman in MN that was about the right age but no results showed up for Missouri.

Name: Wm F Feldman
Age in 1860: 28
Birth Year: abt 1832
Birthplace: Germany
Home in 1860: Oshawa, Nicollet, Minnesota
Gender: Male
Post Office: St Peter
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The 1870 census showed one result for a Wm. Feldman in Missouri, but the birth year is a little later.

William Feldman Saint Charles, St Charles, Missouri
born abt 1837 Prussia

I would need more information about him before I could continue searching. Wife's name? Any children? Did his parents immigrate later?