The Middletown Historic District covers the original core of the town along Main Street and a few surrounding blocks, and was listed on the National Register of Historic Places in recognition of its surviving concentration of 19th-century commercial and residential architecture. The district includes Victorian-era storefronts, Federal-style houses, and a handful of earlier buildings that survived the rapid growth of the surrounding commuter suburbs.
Walking Main Street takes about twenty minutes end to end. The most significant individual building is the old Middletown Academy (now repurposed), a two-story brick school built in the early 19th century that served the community for generations. Several of the Victorian commercial buildings retain their original facades with cast-iron details. The Philip Reading Tannery, a short walk from the main district, is a rare surviving example of the kind of small industrial building that underpinned Delaware's 19th-century economy.