Some of the longest-serving mayors in the United States are listed according to their length of service in that office. The office of mayor is the highest ranking local official and responsibilities may vary from ceremonial (see weak mayor) to full-time responsibility for city operations (see strong mayor).
List of longest-serving mayors in the United States Wikipedia
A list of mayors still in office and ordered by their length of continuous service in that office. (If there is a break in their service, then this length is measured from their return to the office.)
A list of mayors in order of their total length of service in that office. (If there is a break in their service, then this length is measured as the sum of their terms.) John M. Coyne (born 1916) was the mayor of Brooklyn, Ohio from 1948 to 2000, making his term the longest consecutive term of any mayor in the United States until 2008 when Hilmar Moore took over the top spot.