Don't Know if it will help but there was a Cornelius N. McGuire serving in the 1st(Turney's) Tennessee Infantry. All other Cornelius's I could locate served in non-local federal units. It's possible he could have joined up with a union unit from another state, a number of Tennesseeans with unionist sentiments did. Turney's unit was recruited around the Franklin, Bedford, and Grundy county area. If your in Tennessee, the service record should be avialable on microfilm at the following locations- Memphis Public library main branch, Tennessee State Library and archives in Nashville, the McClung collection at the Univ. Of Tennessee in Knoxville, and the Hamilton county public library in Chattanooga. It should give enough biographical info to help determine if he's your man.