The volunteers for Company F were primarily from Buchanan, Delaware and Dubuque Counties.
A few were from Clayton and Winneshiek Counties.
Tommy Joe Fulton and Peggy Hoehne have put a great deal of effort into putting "History of Buchanan County, Iowa 1842-1881" online. They have graciously allowed me to use the letters and other information regarding the 27th on my website. However, if your ancestor was from Buchanan County, you should check it out for any other mention of your ancestor.
Note: these links leave the 27th Iowa website.