Lewis Dillwyn may refer to:

• Lewis Llewelyn Dillwyn (1814–1892), Welsh industrialist and Member of Parliament
• Lewis Weston Dillwyn (1778–1855), British porcelain manufacturer, naturalist and Member of Parliament

• Grasslands Reserve Program
• Grassland suncup
• Grasslands Wildlife Management Area
• Grassland, Texas
• Grassland, TX
• Grass languages
• Grassleaf orache
• Grassleaf sorrel
• Grassleaf Sorrel
• Grass-leaved Golden-aster
• Grass-leaved golden-aster
• Grassley
• Grassman
• Grassman integral
• Grassmann-Cayley algebra
• Grassmann coordinates.
• Grassmannian (disambiguation)
• Grass Mantis
• Grass mantis
• Grass mat
• Grassmere, Ontario
• Grass-miner moth
• Grassmoor railway station
• Grass moth
• Grass moths