HILLS BANCORPORATION EXHIBIT 11 COMPUTATION OF EARNINGS PER COMMON SHARE Three Months Six Months Ended June 30, Ended June 30, --------------------- --------------------- 1999 1998 1999 1998 --------------------- --------------------- Weighted average number of shares outstanding (basic) . 1,484,525 1,467,754 1,476,139 1,467,754 Weighted average of potential dilutive shares attributable to stock options granted computed under the treasury stock method .......................... 11,871 20,563 16,217 21,931 --------- --------- --------- --------- Weighted average number of shares (diluted) ........... 1,496,396 1,488,317 1,492,356 1,489,685 ========= ========= ========= ========= Earnings Per Share: Net income (in thousands) .......................... $ 2,081 $ 1,733 $ 4,160 $ 3,577 ========= ========= ========= ========= Earnings per common share: Basic ............................................ $ 1.40 $ 1.18 $ 2.80 $ 2.44 ========= ========= ========= ========= Diluted .......................................... 1.39 1.16 2.78 2.40 ========= ========= ========= =========