Here's the chronology for the 28th's formation during April and May of that year:
28TH INFANTRY IS FORMED --APRIL AND MAY, 1862
4/1/62 Rifles and cartridges purchased and imported from England by Louisiana Governor Thomas Moore are seized by Florida's Governor Milton.
4/7/62 Union won 2 day Battle of Shiloh, Tn.
4/24/62 Federal fleet passes Ft. Jackson and St, Philip below New Orleans.
4/26/62 Company F, The Jackson Volunteers, began forming at Vernon in Jackson Parish.
4/29/62 New Orleans, La. fell to Union Fleet under Admiral David G. Farragut.
5/1/62 Union General Benjamin Butler took possession of New Orleans, La.
5/7/62 Company K, of Winn Parish began signing up in Monroe.
5/8/62 Company A, The Bienville Stars, and Company H, also of Bienville Parish, signed up in Monroe.
5/10/62 Company C, of Jackson Parish and Company E, Of Winn Parish, sign up in Monroe.
5/11/62 Company D, the Claiborne Invincibles, and Company I sign up in Monroe
5/12/62 Union General Thomas Williams captured Baton Rouge.
5/14/62 Company G, of Winn Parish signed up in Monroe.
For a full timeline of the 28th Infantry and its involvement in the War Between The States, check out this link.