Regiment strength in the Union Army was roughly 1,000 men (infantry & officers). Rarely however were regiments at full strength- disease, sickness, death, desertions, etc. A regiment was typically made up of 10 companies. A company was usually made up of men from the same 1 or 2 towns. Therefore as the war dragged on and casualties mounted, it was not unheard of to have the young male populations of whole communities not return from the war.