Vermont may have more resources on the Civil War proportionately than any other state. Its historical society is very helpful. Another helpful resource is Vermont in the Civil War, Lest We Forget. It is a very handy website with lots of information and some literature on Vermont units. I've found it very helpful in the last few days writing an account of June 23, 1864, possibly the biggest disaster of the Civil War for Vermont, with about 600 casualties, many of whom were captives who perished in southern prisons. Particularly helpful were the letters of Capt. Aldace Freeman Walker, commander of the 2nd Battalion of the 1st Vermont Heavy Artillery (aka 11th Vermont Infantry), and the diary of Walker's subordinate, Second Lieutenant Henry Edson Bedell, who survived the Confederate attack.