He was elected to the post of county executive of Nassau County in 1977. He secured the nomination of the Republican Party over fellow Republican and incumbent county executive Ralph G. Caso, who also opposed Purcell in the general election. He took office in January 1978. In the late 1970s and '80s, Purcell promoted the development of downtown Nassau County businesses, and oversaw the transformation of Mitchel field, a former air base, into a recreational and educational center.
