Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bonemarrow called hemocytoblasts make all of the formed elements in blood. If a hemocytoblast decides to becoming a cell called a proerythroblast, it will develop into a new red blood cell.

The process of a red blood cell from hemocytoblast takes about 96 hours. The body makes about two million red blood cells every second.

They're wayyyy to many rbcs to keep up with so I'm going to name one and follow it.