My paternal grandmother Catherine was an adoptee.
She was born on February 7, 1917 at the St. Vincent Orphan Asylum in Chicago.
Grandma Catherine always knew she'd been adopted, and was not treated differently from her siblings.
My path to identifying her biological parents is long, and amusing, but in 2018 I was able to confirm the names of her biological parents.
Her mother was a woman named Margaret M. born in Iowa County, WI. She was most likely working as a household "domestic" (servant) when she met the man who fathered my grandmother. His name was Edward B., born in Lee County IL to a farming family that had been in the US since the 1860s.
They were both older, single, and it's unclear why Edward did not marry Margaret. They both (separately) moved to Chicago and went on to marry other partners.
Edward had 4 children with his wife, but died young. He was claimed by a heart attack at age 54.
Margaret never had any other children, lost her husband Ernest in 1946, and passed away in 1959 from the same type of Leukemia that took Grandma Catherine's life in 2001.
Grandma Catherine had half-siblings she didn't even know existed. I've been in touch with a few of the children of one of Edward's sons who popped up as matches on AncestryDNA.
I've been in touch with a lot of "cousins" on that family line, and it's been an absolute blast to learn more about them.
Of course there are still some "brick walls" here and there, particularly around Margaret's father (whose journey to America is not clear), but genetic genealogy has provided a few clues.