A few weeks ago the Twins signed a deal to keep their training facility in Fort Myers, Florida through 2020. As a byproduct of this deal, the Twins will likely keep their Florida League affiliate, the Fort Myers Miracle, in Fort Myers. Minnesota and Ft. Myers have had an affiliation since 1993, so they will be wed for at least 28 years if they ever do divorce.
That seems like a long time, but given that their Florida State colleagues, the Lakeland Tigers, have had an affiliation with the Detroit Tigers since 1967, it may not even make their affiliation the longest in their own league by the time their long-term deal ends. It also gives one pause when one considers two other long-time affiliations.
Last year the Twins themselves took on a new Triple-A affiliation with the Rochester (NY) Red Wings, the longest-standing minor league team in baseball history (and Lou Gramm's favorite team). Rochester has been in the International League since 1895, when it was still called the (old) Eastern League and they were the Browns (Note: They did move to Ottawa briefly in 1897). The Red Wings had a long-standing partnership with the Orioles going back to 1961 (42 years in total).
Rochester's and Baltimore's baseball histories had been entangled before. In 1890, the Orioles abandoned the major-league American Association for the Atlantic Association, a new league with designs on becoming a third major league. The Rochester Hop-Bitters replaced them in the AA. At the same time the Brooklyn Bridegrooms, who would later be renamed the Dodgers, moved from the AA to the National League. A new Brooklyn team, the short-lived Gladiators, was added to the American Association.
By July the Atlantic Association had replaced one disbanded team and had shifted another to a new city. When two more teams folded in August, the Orioles decided to move back to the American Association on August 27, replacing the 26-73 makeshift Brooklyn team. The O's went 15-19 the rest of the year but were shackled with the Gladiators abysmal record compiling an overall record of 41-92.
The Orioles eventually moved on to the National League and became the most famous team of the 1890s. The Hop-Bitters moved to the minor-league Eastern League in 1891 and stumbled through two more seasons.
Finally, no mention of Oriole affiliates would be complete without bringing up the Bluefield Orioles of the Appalachian League. The Bluefield O's, a.k.a. the "Baby Birds", have been affiliated with Baltimore since 1958, going on 47 seasons. That is the longest continuous affiliation among current teams and the longest that I have been able to find in major-league history.
Like the Twins, the team that started this dissertation, the Bluefield Orioles represent the twin cities of Bluefield, West Virginia, and Bluefield, Virginia. Their ballpark, Bowen Field (opened 1939), lies exactly on the Virginia-West Virginia border. West Virginia maintains the park even though technically it lies in Virginia.