US Manufacturers by South Dakota
After searching for bicycle manufacturers in South Dakota, there does not appear to be any major professional large-scale bicycle brands manufacturing complete bikes or frames within the state itself. The limited population and demand in South Dakota likely discourages major bicycle production facilities from opening up shop there.
However, there could be some small, custom bike builders or specialty shops constructing bespoke bikes on a limited basis within South Dakota that I could not uncover in my initial research. But no sizable or well-known bike manufacturers seem to call the state home currently.