Grimes is a city in Polk and Dallas counties in the U.S. state of Iowa. The population was 15,392 at the time of the 2020 Census. Grimes is par…Grimes is a city in Polk and Dallas counties in the U.S. state of Iowa. The population was 15,392 at the time of the 2020 Census. Grimes is part of the Des Moines-West Des Moines metropolitan area. Grimes incorporated as a city on May 7, 1894. It is named after James W. Grimes, a former U.S. senator and the third governor of Iowa.