Delaware Route 299 (DE 299) is a 9.77-mile-long (15.72 km) state highway in New Castle County, Delaware. It runs from Maryland Route 282 (MD 282) at the Maryland state line east of Warwick, Maryland to DE 9 in Mathews Corners, traveling through Middletown and Odessa. The route intersects the U.S. Route 301 (US 301) toll road, DE 15, and DE 71 in Middletown, the DE 1 toll road east of Middletown, and US 13 in Odessa. The highway travels through a mix of suburban development and some farmland.

New Castle County is the northernmost of the three counties of the U.S. state of Delaware. As of the 2020 census, the population was 570,719, making it the most populous county in Delaware, with nearly 60% of the state's population of 989,948. The county seat is Wilmington, which is also the state's most populous city.