Please check out the Wisconsin Veterans Museum in Madison, Wis. They have a website for research and documents you maybe able to research the documents you need with Russ help. They have a wonderful civil war collection on Wisconsin Civil war units. Please copy and paste this link into your web browser. Follow at the bottom of the page and click on the items you want to view. Such as history, rosters, casualties, and documents.
Hope this helps,
Dear Mr. Janecek,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located Regimental and Company Books of Civil War Volunteer Union Organizations, 1861 - 1867 in the Records of the Adjutant General's Office, 1762 - 1917 (Record Group 94) that contains Regimental and Company Books of the 18th Wisconsin Infantry Regiment. We also located the Compiled Records Showing Service of Military Units in Volunteer Union Organizations in Record Group 94 that have information about the unit. Also, though you stated you are researching the unit as a whole rather than individuals, looking at some of the records regarding individuals may provide some insights. In addition, we located some digitized service and pension records in Record Group 94 for soldiers of the 18th Wisconsin Infantry Regiment that are available online using the Catalog. There may be additional files that have not been digitized yet. For further information about these records, please email the National Archives at Washington, DC - Textual Reference (RDT1) at Archives1reference@nara.gov.
Next. we located 76 record series with varying degrees of information about Wisconsin units at the National Archives at Chicago (RM-CH). Please email RM-CH at firstname.lastname@example.org for more information.
For additional records series and other resources that may have information about the unit, see our blog post Records Relating to Civil War Units.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT1 and RM-CH. We apologize for this inconvenience and appreciate your understanding and patience.
Plus we searched the Civil War Soldiers and Sailors System (CWSS) and located an entry for the 18th Regiment, Wisconsin Infantry.
We hope this is helpful. Best of luck with your research!