The Third Principal Meridian
Centralia, Illinois

This point was established in 1815 and is the cornerstone of 60% of the land in Illinois including Chicago. 

Once the original point was established and new corner points were surveyed, new land was physically referenced to the nearest corner point. As a result, this point was no longer needed and covered by an expansion of highway 51. In 1976 a project was undertaken to rediscover the original corner stone. It was  under the highway exactly where it was supposed to be. The spot is now covered with a removable steel plate.


Home Page

Submitted by:

John N Shankland


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Historical Marker

Because the original marker is buried under route 51 this marker replaces it with an an exact offset to the original.

This satellite picture clearly shows the effect of grid surveying.
The 3rd PM is on highway 51 to the right of the red dot. To the left is the Rock Island Railroad. Centralia IL is above