John III, Count of Oldenburg

John III (documented 1302–1342) was Count of Oldenburg, the second son of Count John II and Elisabeth of Brunswick-Lüneburg. From 1316 he ruled jointly with his brother Christian IV, and from 1324 with his half-brother Conrad I. At his order the illuminated Rastede manuscript of the Sachsenspiegel, the medieval Saxon law book, was completed in 1336.

With Conrad he joined the Archbishop of Bremen in war against the Rüstringen Frisians until peace in 1337. He died in 1342, leaving his son John IV to succeed him.