Here’s the link https://history.army.mil/faq/branches.htm.
This was inspired by my re-blog There’s More Than One Way to Shoot in a War — Pacific Paratrooper.
In the first link, June 21, 1860 is the birthday given for the Signal Corps https://history.army.mil/faq/SigCpsGO.htm.
I have been working on a list of U. S. Miltary unit birthdays for a while now. This link helped me out a lot as it includes units I had not found starting dates. I will look for other branches on similar sites to see if they list unit starting dates I am still looking for. In some cases, I only have a general year when a specific unit type started.