| 1 | Amy Feddersen SR | Ames | 55.56 | Ames High School | 10/02/2018 |
| 2 | Berit Quass JR | Dowling Catholic | 56.68 | Summit Middle School | 10/18/2018 |
| 3 | Katie Broderick JR | Dowling Catholic | 56.82 | Ames High School | 10/10/2018 |
| 4 | Annie Galvin SO | Ames | 57.70 | Ames High School | 10/10/2018 |
| 5 | Grace Frericks FR | Cedar Falls | 58.00 | Linn-Mar High School | 09/08/2018 |
| 6 | Emily Van De Wiele SR | Bettendorf | 58.21 | Linn-Mar High School | 09/08/2018 |
| 7 | Sami Roemer JR | Bettendorf | 58.70 | Mercer Park Aquatic Center and Scanlon Gym | 09/15/2018 |
| 7 | Zoe Pawloski SR | Lewis Central | 58.70 | Valley High School | 09/22/2018 |
| 9 | Mary Martin SO | Dowling Catholic | 58.72 | Summit Middle School | 10/18/2018 |
| 10 | Abby Hala FR | Ames | 58.94 | Ames High School | 10/10/2018 |
| 11 | Abby McCorkle SO | Ames | 59.03 | Ames High School | 09/18/2018 |
| 12 | Hope Cvrk SO | Sioux City, North | 59.36 | Spencer Family YMCA, 11th Avenue West, Spencer, IA | 10/16/2018 |
| 12 | Arabella Shepard SR | Vinton-Shellsburg | 59.36 | Natatorium | 10/13/2018 |
| 14 | Ellie Clark SO | Dowling Catholic | 59.65 | Fort Dodge Senior High School | 09/15/2018 |
| 15 | Sarah Grochala SO | Dowling Catholic | 59.84 | Summit Middle School | 10/18/2018 |
| 16 | Aurora Roghair SO | Iowa City, West | 1:00.01 | Washington High School | 08/28/2018 |
| 17 | Carly Weigel JR | Iowa City, City High | 1:00.08 | Linn-Mar Aquatic Center | 10/13/2018 |
| 18 | Scout Bergwall JR | Ankeny | 1:00.20 | Indianola YMCA | 09/04/2018 |
| 19 | Sydney Jones SO | Cedar Rapids, Washington | 1:00.21 | Kennedy High School | 10/20/2018 |
| 20 | Victoria Michel JR | Wahlert, Dubuque | 1:00.22 | San Jose Swimming Pool | 08/21/2018 |
| 20 | Alexis Henning FR | Ankeny | 1:00.22 | Summit Middle School | 10/09/2018 |
| 22 | Luanne Xiao JR | Fort Dodge | 1:00.28 | Linn-Mar High School | 09/08/2018 |
| 23 | Erin Doruska SR | Ankeny | 1:00.30 | Indianola YMCA | 09/04/2018 |
| 23 | Megan Latta SR | Dowling Catholic | 1:00.30 | Summit Middle School | 10/18/2018 |
| 25 | Caroline Schultz SO | Dowling Catholic | 1:00.33 | Trail Point Aquatics & Wellness | 09/25/2018 |
| 26 | Jasmine Rumley JR | Ankeny | 1:00.37 | Summit Middle School | 10/18/2018 |
| 26 | Grace Veach FR | Pleasant Valley | 1:00.37 | Linn-Mar High School | 09/08/2018 |
| 28 | Emma VerSteeg SR | Spencer | 1:00.47 | Spencer Family YMCA, 11th Avenue West, Spencer, IA | 10/16/2018 |
| 29 | Abby Rastetter SO | Johnston | 1:00.55 | Marshalltown High School | 09/15/2018 |
| 30 | Maddie Grant JR | Dowling Catholic | 1:00.57 | Summit Middle School | 10/18/2018 |
| 31 | Kate MacLeod SO | Ames | 1:00.58 | Ames High School | 10/10/2018 |
| 32 | Anna Hamling JR | Waukee | 1:00.62 | Fort Dodge Senior High School | 09/18/2018 |