Ransom Eli Olds, for whom both the Oldsmobile and REO brands were named, is credited with designing the basic concept of the assembly line. At the Old Motor Works in Detroit he mass produced the Curved Dash Oldsmobile becoming the leading American auto producer from 1901 through 1904.  By 1901 Olds had built 11 prototype vehicles, including at least one of each power mode: steam, electricity and gasoline.

Olds was the first person to use a stationary assembly line in the automotive industry. Henry Ford came after him, and was the first to use a moving assembly line to manufacture cars. Henry Ford perfected the assembly line producing a entire Model T Ford in 93 minutes.

Michigan Yesterday & Today. Voyageur Press. Page 29
https://books.google.com/books?id=HQdTa9ZXlVAC&pg=PA29#v=onepage&q&f=false