The Ohio River is a major U.S. inland waterway. It forms the Ohio–West Virginia, Ohio–Kentucky, Indiana–Kentucky, and Illinois–Kentucky state lines. By extension, it also forms the boundary of all counties and townships and many municipalities along the river. This page exists to call attention to a common oversight by OpenStreetMap contributors. Please note:
State lines do not follow the Ohio River's present-day thalweg.
In January 1980, the U.S. Supreme Court ruled that the state line is the low-water mark of the Ohio River's north shore as of Kentucky's admission to the Union in 1792.  Because both damming and natural changes have rendered the 1792 shore virtually undetectable in many places, the exact boundary was decided in the 1990s in settlements among the states.  The settlements gave the northern states a minimum clearance into the river, as measured from the present-day north shore, allowing them to collect revenue from fishing and riverboat gambling. Kentucky and West Virginia own all or nearly all of the river islands, even the ones located nearer to Ohio than West Virginia.
The state lines were originally imported from the USGS county boundary data set, which was accurate in many places but sometimes jogged outside the river due to low resolution. By 2014, the state lines had mostly been conflated with higher-resolution ways representing the Ohio River's thalweg, in contradiction to the court ruling and settlements.
The state lines are gradually being redrawn based on the USGS Topographic Maps layer. In most places, this layer is current as of around 1980, when the dispute first resurfaced. Therefore, our source is based on the 1792 northern low-water mark but not necessarily the 1990s settlements. There are some significant implications:
- Vevay Island (a former island near Vevay) is shown as part of Kentucky, but it is now part of Indiana. On the other hand, Green River Island (a former island near Evansville) is mostly part of Kentucky, as shown in USGS maps. 
- Per USGS policy on disputed boundaries, the Ohio–West Virginia border simply vanishes around disputed islands such as Vienna Island near Parkersburg.  Some islands, such as Buffington Island near Ravenswood, lie adjacent to an "Indefinite Boundary".
- Due to shifts in the river since the topo maps were produced, the boundary occasionally runs slightly aground in Ohio, despite the minimum clearance mentioned above.
If you know of a more up-to-date, appropriately licensed source for this boundary information, please e-mail the talk-us mailing list.
Administrative boundaries have been corrected from the Ohio–Pennsylvania–West Virginia tripoint all the way to Cairo, Illinois. However, the boundaries run aground in Indiana and Illinois in several places and need to be corrected to their present-day path. Please pitch in!