| Birth Date: | 18 April 1920 |
| Birth Place: | Budapest, Austria-Hungary |
| Death Place: | Budapest, Hungary |
Ilona Ács (later Zimmermann; April 18, 1920 - November 23, 1976) was a Hungarian freestyle swimmer who competed in the 1936 Summer Olympics. She was born and died in Budapest. In 1936 she was a member of the Hungarian relay team that finished fourth in the 4 x 100 metre freestyle relay event. In the 100 metre freestyle competition she was eliminated in the first round.