- Western Terminus:
- Main Street (MD 282) at the Maryland-Delaware state line
- Eastern Terminus:
- Taylors Bridge Road (DE 9) and Thomas Landing Road (DE 9) in Middletown
- 9.16 miles
- New Castle
DE 299 is an east/west route through Middletown and Odessa. Main Street (MD 282) turns into Warwick Road upon entering Delaware. It runs next to the US 301 toll highway in the area of the cashless tolling gantries. Just beyond the toll, Warwick Road curves to the southeast and crosses the highway at its first interchange. Immediately thereafter, Warwick Road ends at a traffic light at Levels Road (DE 15) and Middletown Warwick Road, the old alignment of US 301 from before the construction of the toll highway. DE 299 and DE 15 both turn onto Middletown Warwick Road. The two routes are multiplexed for a little over a mile, and then they split. DE 299 turns to the east onto Main Street, while DE 15 turns to the west onto Bunker Hill Road.
Main Street passes through the downtown area of Middletown and then changes names to become Middletown Odessa Road. There is an interchange with the DE 1 toll highway. Then, DE 299 passes through Odessa, where it is known as Main Street again and crosses Dupont Parkway (US 13). Upon leaving Odessa, Main Street becomes Old State Road. After a little less than a mile, DE 299 turns onto Taylors Bridge Road. After one block, it ends at the intersection where DE 9 turns from Taylors Bridge Road onto Thomas Landing Road.
Most of Warwick Road as it exists today was constructed in conjunction with the US 301 toll highway. In the days before the toll highway, Warwick Road ended at Middletown Warwick Road, which was then US 301, just after crossing the state line from Maryland. DE 299 was multiplexed with US 301 along Middletown Warwick Road north to the point where Warwick Road ends today. The remainder of its alignment was the same as it is today.