In 1882, with the help of his father in-law, Mathias Wagner, Thedieck made plans for his future retailing empire. Wagner purchased the lot to the north of the court house on Poplar Street to build the most modern shopping facility in town. Young Thedieck shared the newly constructed space equally with his brother in-law, William Wagner.

Virtually from the beginning, Thedieck's vision of retailing encompassed far more than just selling to the Sidney trade. 'Mom and Pop' stores dotted the retailing landscape in the 1880s. Branch stores were virtually unknown. However, Thedieck began to establish stores in nearby villages and towns. The March 14, 1884, edition of the Sidney Journal carried the news that "Thedieck Bros. will soon open a large dry goods store at Piqua. The Piqua store will be the fifth...(with other) stores at Sidney, Lima, St. Marys and Minster." In an understatement, the editor described the brothers as "energetic businessmen."

By employing hard work and novel marketing efforts, Thedieck built a thriving business. In 1884 he advertised in the Shelby County Democrat that "A Crash Is Coming!" and promised to slash prices on goods he had imported from New York by 25 to 50 percent. It wasn't long before his business, now called the Thedieck Department Store, expanded to occupy the entire structure.