Starting at the Prime Meridian and heading eastwards, the parallel 40° north passes through:
|Country, territory or sea||Notes|
|Island of Minorca|
|Island of Sardinia|
|Mediterranean Sea||Tyrrhenian Sea|
|Mediterranean Sea||Gulf of Taranto|
|Mediterranean Sea||Strait of Otranto|
|Aegean Sea||Including the Kassandra and Sithonia peninsulas, and the island of Lemnos ()|
|Sokh exclave surrounded by|
|Shakhimardan exclave surrounded by|
|Yellow Sea||Liaodong Bay|
|Sea of Japan|
|Island of Honshū|
Nebraska / Kansas border
The parallel 40° north formed the original northern boundary of the British Colony of Maryland. A subsequent royal grant gave the Colony of Pennsylvania land north of the parallel 39° north. The Mason-Dixon Line was drawn between 1763 and 1767 as the compromise boundary between the overlapping claims of these two colonies.
The parallel 40° north passes through the cities of Philadelphia, Pennsylvania and Columbus, Ohio; as well as northern suburbs of Indianapolis, Indiana and Denver, Colorado. The parallel goes directly through the Port Columbus International Airport, with runway 10L-28R lying immediately north of the line, runway 10R-28L lying slightly south of it, and the line going through the northernmost edges of the terminal.