What was the bloodiest battle in the US Civil War?

There is no question that the three day battle of Gettysburg caused more total casualties than the one day Battle of Antietam. The casualty count varies, as one can understand that record keeping in those days of war could never be exact, and add to that the unknown number of deserters. Generally speaking, however, Union war records are more reliable concerning their own troops. Records kept in Richmond for troop casualties are not as reliable.

With that said, and speaking in terms of the actual question, Gettysburg yielded an estimated range of casualties that numbered between 46 to 54,000 in total.

The Battle of Antietam, the single largest one day number of total casualties of any US battle in US history yields an estimate ranging from 22 to 26,000 thousand.

There are multiple sources that yield ranges that differ from one degree or another. However, clearly the three day Battle of Gettysburg with more troops in total to begin with was indeed the bloodiest US Civil War battle.

The Battle of Antietam is the bloodiest battle from what I've read! Hope that answers your question.

Battle Of Antietam 100 percent TRUE

Antietam is the bloodiest single day battle. Gettysburg is the bloodiest battle overall.
The bloodiest battle in the Civil War was the second Bull Run Battle.