 What would become DE 1 between Milford and Rehoboth Beach was originally a county road by 1920. By 1924, the road was proposed as a state highway between Nassau and Rehoboth Beach. A year later, the state highway was completed between Milford and Cedar Creek and from Nassau to just west of Rehoboth Beach, with the sections between Cedar Creek and Nassau and into Rehoboth Beach under proposal. In 1927, the state highway between Milford and Rehoboth Beach was completed with the construction of a bascule bridge over the Broadkill River. In 1931, a state gravel road was extended from Bethany Beach to the Indian River Inlet, providing access to the inlet for recreational purposes. In January 1933, bids were made for construction of a gravel road from Dewey Beach south to the Indian River Inlet as well as for a timber bridge across the inlet, connecting with the gravel road between the Indian River Inlet and Bethany Beach. This gravel road would provide a direct connection between Bethany Beach and Rehoboth Beach and would provide better access to the Atlantic coast for recreation. The Ocean Highway between Bethany Beach and Rehoboth Beach was completed in 1933. In fall of that year, the roadway between Bethany Beach and Indian River Inlet was paved, with recommendations to pave the road north from the Indian River Inlet toward Rehoboth Beach. In 1934, the Ocean Highway between the Indian River Inlet and Rehoboth Beach was paved. The same year, recommendations were made to extend the Ocean Highway south from Bethany Beach to Fenwick Island, where it would lead to a Maryland state highway continuing to Ocean City.
