score:20
There was a lawsuit between Frankfurt and Hanau which lasted some 212 years.
In the late 16th century, a dispute broke out between the Free Imperial City of Frankfurt and its neighbour the County of Hanau over rights to a wine tithe. The tithe was formerly owed by the farmers of Hanau to the abbess of the White Ladies Convent in Frankfurt, but the city became Lutheran during the Reformation and secularised the convent. After the last abbess passed away in 1588, both the municipal government of Frankfurt and the Count of Hanau laid claim to the tithe.
In 1594, Frankfurt and Hanau brought their dispute before the Reichskammergericht. Instituted in 1495 as the Holy Roman Empire's highest judiciary, the Reichskammergericht gained a reputation for being extremely slow in reaching a final verdict, with cases routinely taking decades to be resolved. By the time it came to an end, it had such a massive backlog that it was joked the court hung the files up, and attend to them as they fall to the ground (due to mice chewing on the strings).
Their case would remain pending in court for the next 212 years, until the Reichskammergericht was dissolved along with the Holy Roman Empire itself in 1806.
Reference:
Seidl-Hohenveldern, Ignaz. "Extraterritorial Respect for State Acts." Hague Yearbook of International Law. Hague Academy of International Law. Association of Attenders and Alumni. The Hague: Martinus Nijhoff, 1988.
Upvote:3
The "pleitos colombinos" the series of suits, decisions and appeals between the Crown of Spain and Christopher Columbus and his descendants (as well as between his descendants) lasted from 1516 until (at least) 1792, when the matter was still being argued before Spanish courts. This gets the year count up to 276.
References:
Mariano Colón de Toledo y Larreátegui, Información juridica en grado de segunda suplicación. (Madrid: 1792)
De los Pleitos de Colón. vols 7 and 8 of Colección de documentos ineditos relativos al descubrimiento, conquista y organización de las antiguas posesiones españolas de ultramar. 2. ser. Madrid, Est. tip. "Sucesores de Rivadeneyra," 1885.
Upvote:9
The longest running that I can find is the property dispute of Raja Rajkrishna Deb, which was started in 1833 and is as far as I can find still pending after 181 years.