Except as provided by Section 10-20, when 2 or more townships, any one or more of which possess or are entitled to moneys, rights or credits, or other personal estate, are united, or when a township possessing or entitled to moneys, rights or credits, or other personal estates is divided or altered, the personal estate, including moneys, shall be apportioned between the townships interested in that personal estate by the supervisors and assessors of the townships according to the amount of taxable property in the township or townships united, divided, or altered as that amount existed immediately before the union, division, or alteration. That amount shall be ascertained by the last assessment list of the township or townships. The supervisors and assessors shall meet for this purpose as soon as may be practicable after the union, division, or alteration.