N.Y. County Law § 280-y

§ 280-y. Extension of the district. A county district may be extended\nso as to include territory not previously included within its boundaries\nin the same manner as hereinbefore prescribed for the original\nestablishment of the district. If the cost of establishment af the\noriginal district and of providing the improvement therein was assessed,\nlevied and collected pursuant to the provisions of section two hundred\neighty-u, then the cost of the extension and of the improvements therein\nshall be assessed, levied and collected pursuant to the provisions of\nsaid section. If the cost of establishment of the original district and\nof providing of the improvement therein was assessed, levied and\ncollected pursuant to the provisions of section two hundred eighty-v,\nthen the cost of the extension and of the improvement therein shall be\nassessed, levied and collected pursuant to the provisions of said\nsection. The cost of the extension shall include such proportion of the\ncost of the system of the original district as the governing body shall\ndetermine.\n