Prior to 1909, the center of Chicago's address system was Wolf Point, with N/S and E/W addresses divided by the Chicago River.

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West of the river, North/South addresses were split by Lake St, which is just south of the main branch. The E/W boundaries moved with the river, making things pretty inconsistent.

Even more confusing, south of the main branch of the river, East addresses started with 1E at Lake Michigan and increased as you moved West, but north of the main branch, increased as they do now, moving eastward.

The center of the grid is now at State & Madison.