53 Pa. C.S. § 8822
(a) General rule.--Except as provided in subsections (b) and (c), if a taxing district lies in more than one county and the respective counties fix different predetermined ratios for the assessment of property, the following shall apply:
(1) The taxing district may levy its taxes on the ratio to actual value used by any one of the counties.
(2) A county, other than the county whose predetermined ratio has been selected in accordance with paragraph (1), shall certify to the taxing district a copy of the assessment roll which shows the actual valuations of properties within the county's portion of the taxing district, so that taxes to be levied on the property may be calculated using the assessed valuation determined by applying the selected predetermined ratio to actual valuation of the property.
(b) Multiple counties.-- In the case of school districts lying in more than one county, section 672.1 of the act of March 10, 1949 (P.L. 30, No. 14), known as the Public School Code of 1949, shall apply.
(c) Annexation.--If land in one county has been annexed to a borough in another county, the following shall apply:
(1) For county tax purposes, the lands and properties within the borough shall be assessed by the county assessment office of the county in which the lands and properties are located.
(2) For borough and school tax purposes, all lands and properties within the borough, regardless of the county in which they are located, shall be assessed by the county assessment office of the county that assessed lands and properties within the borough prior to the annexation.
53 Pa.C.S. § 8822