In order to determine the couple in my family tree who was married the longest, I need to know two things: 1) when they were married and 2) when at least one of them died. So just looking at my direct ancestors who meet that criteria, the couple married the longest is my paternal Great Grandparents, Clarence & Cora Mann. Married in Fairbury, Nebraska on July 5, 1899, they were married for 69 years until his death in October, 1968. I'm not sure, but it seems like I remember hearing that their anniversary was mentioned by Paul Harvey on his radio show. The Lincoln Journal Star even published an article about their anniversary in July of 1968. In 1949, they got their picture in the paper for their 50th anniversary. Such media moguls!
Less attention was probably given to my Seventh Great Grandparents Ebenezer Bliss & Joanna Lamb. They were married in Springfield, Massachusetts on July 23, 1723 and until his death in November of 1761 - over 38 years. They are also the Fourth Great Grandparents of Cora Mann.
On July 2, 1648, Thomas Sawyer married Mary Prescott in what is now Lancaster, Massachusetts. Thomas died in 1706, so they were married for 58 years. They are my Eighth Great Grandparents. Their marriage is recorded in various books of transcribed Vital Records from Massachusetts towns.
The stats for July are 49 marriages, the 11th is the most popular date with four marriages on that day. Probably not all of them got the media attention that Clarence & Cora Mann did.