X0306 4 2017-06-12 0000723188 COMMUNITY BANK SYSTEM, INC. CBU 0001485474 Mucenski Edward S. C/O COMMUNITY BANK SYSTEM, INC. 5790 WIDEWATERS PARKWAY DEWITT NY 13214 1 Common Stock 2017-06-12 4 M 0 850 27.36 A 3185.98 D Common Stock 2017-06-12 4 M 0 2150 28.78 A 5335.98 D Common Stock 2017-06-12 4 S 0 3000 57.9612 D 2335.98 D Common Stock 7483.079 I By PMHV 401(k) Plan Common Stock 1526.47 I By Spouse Stock Option 27.36 2017-06-12 4 M 0 850 0 D 2011-01-19 2021-01-19 Common Stock 850 0 D Stock Option 28.78 2017-06-12 4 M 0 2150 0 D 2012-03-21 2022-03-21 Common Stock 2150 2416 D Phantom Stock (Deferred Compensation) Common Stock 9052.233 9052.233 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $57.925 to $57.99, inclusive. The reporting person undertakes to provide Community Bank System, Inc., any security holder of Community Bank System, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. Each unit of phantom stock is the economic equivalent of one share of Community Bank System, Inc. common stock. The units of phantom stock relating to the Deferred Compensation Plan will be settled in Community Bank System, Inc. common stock at future dates selected by the reporting person. Includes 66.8622 units of phantom stock acquired on April 10, 2017 under the Deferred Compensation Plan's dividend reinvestment feature. /s/ Danielle M. Cima, pursuant to a Confirming Statement executed by Edward S. Mucenski 2017-06-13