The KFA's Incheon section made the purchase at around $205.70 a tonne on a cost and freight (c&f) basis for arrival in South Korea around Dec. 5, they said.
The corn was said to be optional United States or South American origin. If sourced from South America, shipment was between Sept. 26 and Oct. 25.
The seller was believed to be trading house CHS.
The KFA's Busan section had also held private negotiations about corn buying late on Tuesday but was not thought to have made a purchase after Chicago corn futures rose sharply.
Chicago July corn rose 2.5% on Tuesday to a one-week high after the US Department of Agriculture (USDA) cut its forecast of US corn crops.
Two other South Korean groups made corn purchases on Tuesday before the USDA report.
Feed maker NOFI purchased some 68,000 tonnes at $206.74 a tonne c&f plus an extra $1.25 a tonne surcharge for additional port unloading.
The Major Feedmill Group purchased about 70,000 tonnes at $206.99 a tonne including a surcharge for additional port unloading.