Delaware Route 12 (DE 12) is a state highway in Kent County, Delaware. It runs from Maryland Route 314 (MD 314) at the Maryland border near Whiteleysburg, Maryland east to an interchange with DE 1 near Frederica. The route follows a mostly rural alignment, passing through the towns of Felton and Frederica. DE 12 intersects U.S. Route 13 (US 13) in Felton and DE 15 east of Felton. What would become DE 12 was built as a state highway during the 1920s. DE 12 was designated between Felton and Frederica by 1936 and extended west to Maryland by 1938. The eastern terminus was moved to its current location in 1965 when US 113 (now DE 1) was routed to bypass Frederica. The DE 1 intersection became an interchange in 2011.

DE 12 begins at the Maryland border, continuing west into that state as MD 314 at the state line. From the state line, the route heads southeast on two-lane undivided Whiteleysburg Road for a short distance before turning northeast onto Burnite Mill Road. The road heads through farmland with some woods and homes, curving east and heading into Felton. At this point, DE 12 becomes Main Street and heads into residential areas, crossing Norfolk Southern's Delmarva Secondary railroad line. The road passes more homes as it comes to an intersection with US 13 on the eastern edge of Felton. Upon leaving Felton, the route becomes Midstate Road and continues through agricultural areas with some homes. DE 12 intersects DE 15 and runs through farmland with some woods and homes, coming to an intersection with Andrews Lake Road, where the name changes to Johnnycake Landing Road. The road passes through more rural areas with some residences before entering Frederica, where it becomes Front Street and is lined with homes. In the eastern part of town, the route splits into the one-way pair of David Street eastbound and Front Street westbound, passing residences along with a few businesses. DE 12 turns north onto two-way Frederica Road and leaves Frederica, passing through marshland and crossing a branch of the Murderkill River. DE 12 continues to its eastern terminus at an interchange with DE 1.

DE 12 has an annual average daily traffic count ranging from a high of 5,207 vehicles where it intersects Frederica Road from the west to a low of 2,204 vehicles at the eastern terminus at DE 1. None of DE 12 is part of the National Highway System.

By 1920, what is now DE 12 existed as an unimproved county road. By 1924, the route was completed as a state highway between Hollandsville and Frederica and was proposed as a state highway between the Maryland border in Whiteleysburg and Hollandsville and within Frederica. The entire road between Whiteleysburg and Frederica was built as a state highway by 1925. When Delaware created its state highway system by 1936, DE 12 was assigned to run from US 13 in Felton to US 113 in Frederica. By 1938, DE 12 was extended west to the Maryland border in Whiteleysburg. In 1965, US 113 was moved to a bypass to the east of Frederica, and DE 12 was extended north on the former alignment of US 113 to end at that route a short distance north of Frederica. In November 2009, construction began for a grade-separated interchange between at DE 1; the interchange was completed in June 2011.

The entire route is in Kent County.