Hi (you do not tell us your name...)
In the Onlinefindbook from the Staatsarchive Niedersachsen http://aidaonline.niedersachsen.de/
they have these entries: (just type Kielhorn Dedenhausen into the search field)
1. Kielhorn, Heinr., Dedenhausen 3. Landwirt 7. Amerika 8. 1863
1. Kielhorn, Heinrich Friedrich, Dedenhausen 7. Amerika 8. vor Nov. 1866
Means: The person is from Dedenhausen (belongs to Uetze close to Hannover), emigrated to America in 1863 and the second date means before (vor) November 1866
Greetings from Germany, Andrea (Korbanka)