By 1920, what would become DE 30 existed as a state highway between
Mission and Phillips Hill and was proposed as one between Phillips Hill and Millsboro, with the remainder of the route existing as a county road. The state highway between Phillips Hill and Millsboro was completed by 1924. The state highway portion was extended from Mission to
Gumboro a year later, with a section in the Gumboro area under proposal as a state highway. By 1931, the road was completed as a state highway between
US 13 and Jones Branch and from James Branch to Gumboro. In addition, the state highway was completed from Millsboro to north of Gravel Hill as an
unpaved road, with a portion north of Gravel Hill becoming a paved county road. The state highway between US 13 and Gumboro was fully complete the following year. By 1936, the road between Millsboro and Gravel Hill was paved. DE 30 was first designated in 1936 to run from DE 20 in
Seaford north and east to DE 404 northwest of
Bridgeville, heading north and crossing
DE 18 in
Atlanta before turning east to reach DE 404. This was eliminated by 1938, and is now Atlanta Road and Dublin Hill Road. By 1938, DE 30 was designated to run from DE 24 in Millsboro north to DE 5 in Milton, following its current alignment to north of Gravel Hill and then running along Shingle Point Road north into Milton. A portion of current DE 30 south of the DE 16 intersection was paved a year later. By 1952, the current route of DE 30 north of Gravel Hill was paved. DE 30 was rerouted to follow its present alignment north to
DE 14 (now DE 1) south of Milford by 1971. By 1994, DE 30 was extended west from Millsboro to Bi-State Boulevard between
Laurel and
Delmar. The route ran concurrent with DE 24 through Millsboro along Main Street and Washington Street before following Millsboro Highway to Mission, where DE 24 split to the west. DE 30 continued south to Shaft Ox Corner, where it joined
DE 26 in a concurrency. In Gumboro,
DE 54 joined DE 26/DE 30 on Millsboro Highway before DE 30 split west along Whitesville Road. The route continued west and crossed US 13 before becoming Dorothy Road and ending at Bi-State Boulevard. The northern terminus of DE 30 was moved to its current location at DE 1 Bus. by 2003 when a road connecting DE 30 to DE 1 Bus. was completed. In November 2012, construction began on an interchange at DE 1 southeast of Milford. The interchange between DE 1 and DE 30 was completed in July 2014. On February 29, 2016, construction began on a
superstreet intersection at US 13; this project was completed on May 19 of that year. In 2021, the
Delaware Department of Transportation (DelDOT) proposed eliminating the portion of DE 30 west of Millsboro. The elimination of this portion of the route was proposed to remove the concurrencies DE 30 had with other numbered routes along Millsboro Highway, reducing sign clutter and motorist confusion. In addition, the section of DE 30 west of Millsboro Highway had no shoulders, low traffic volumes, and ended at a minor intersection with Bi-State Boulevard; the removal of this section of DE 30 may redirect long-distance and truck traffic to use DE 24, DE 26, and DE 54 instead, which have higher traffic volumes and full-width shoulders. The decommissioning was completed in September 2022. There are plans to construct a
roundabout at the DE 16 intersection near Milton in order to reduce crashes at the intersection. Construction of the roundabout is planned for 2025. ==Major intersections==