I have no information that says Jacob was ever in Iowa. I simply have the unlikely match of his name and a wife named Celinda. So I list the following information:
There is a widow's application for Civil War benefits by wife Celinda A. Clark from the State of Iowa. It appears to be 12 Mar 1889. Served: G 17 Iowa Inf.

http://www.interment.net/data/us/ia/dallas/mowrer.htm
Contributed by Frank Stanley, Jun 08, 2000 [stanley@workmail.com]. Total records = 73.
Mowrer Cemetery, established in 1865. Dallas County, Iowa
Ollom, Jacob, "No Dates", Veteran {GAR}