Williamson, a left-handed pitcher who has signed with Michigan State University, is ranked 18th on the list of 75 players.
Ball, a first baseman who has signed with Dallas Baptist University, is ranked 55th.
Williamson was 4-1 with one save with a 3.86 earned run average in 2017 in 49 innings pitched. Williamson had 45 strikeouts and 25 walks as a freshman.
Ball hit .419 for the Trojans during his freshman campaign and earned first-team all-NJCAA Region XI honors. He had 22 doubles with seven home runs, 52 RBIs and scored 49 runs.
Other Iowa junior college players on the Perfect Game list are Kirkwood shortstop Kory Howell, who is ranked fourth, and Iowa Western right-handed pitchers Indigo Diaz (14th) and Keaton Winn (21st).
Howell has committed to Iowa while Diaz has committed to Michigan State and Winn has committed to Mississippi State.