55 ILCS 5/1-3007
All the property, both real and personal, and all debts, liabilities and choses in action of every kind, belonging to the county or counties from which such new county was formed, shall be divided by the several county boards of the counties interested, between the county or counties from which such new county is formed and the new county, in proportion to the assessed value of property for the last preceding year which has been taken from such original county or counties and carried to such new county; and if such boards cannot agree upon such division, they may refer the matter of difference to arbitrators, or the rights to such property may be settled by a civil action filed by either party for that purpose. In case the property cannot be divided or removed, the county receiving the same shall pay to the other a proportionate value for the same.
55 ILCS 5/1-3007