There seems to be a great disparity between different states as to the accessibility of regimental and/or company rosters for Civil war units.
In all my reseaching so far, I find the best are for Tennessee and Illinois. For Tennessee, tngenweb.org is excellent, just about all one would need, USA and CSA alike.
http://www.tngenweb.org/civilwar/tncwindex.html
For Illinois, it is hit and miss. There are several sources, but each has it'sdrawbacks.
The Illinois Civil War Project is one
Illinois in the Civil War has a search function that doesn't work
Illinois Civil War Muster and Descriptive Rolls Database has a search function that does work.
I have expected at least as good as these for NewYork, and other states, but can't find such.
If you know any, why don't you all suggest sources of these kinds of rosters which you have found useful for as many states as you can.
We could wind up with a nice list for folks to work from.
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