score:11
There isn't really a bright line distinction, but John of Damascus (died ~750) is often cited as the last one. For example, Catholic.com:
the death of St. John Damascene [cir. A.D. 750] is generally regarded as the close of the age of the Fathers
The Catholic encyclopedia takes a somewhat nuanced approach, allowing for the suggestion of some later medieval authors, but ultimately prefers John as the last:
"The Fathers" must undoubtedly include, in the West, St. Gregory the Great (d. 604), and in the East, St. John Damascene (d. about 754).
St. John of Damascus (c. 750) closes the patristic period with his polemics against heresies, his exegetical and ascetical writings, his beautiful hymns, and above all his "Fountain of Wisdom", which is a compendium of patristic theology and a kind of anticipation of scholasticism. [emphasis added]
It's perhaps worth noting that while the title of "Father" is no longer applied, the Catholic Church continues to recognize important contributors to theology/doctrine, calling them "Doctors of the Church." The most recent of these, Thérèse of Lisieux, died in 1897.