Wikipedia served as the source for the population information. Note that the population increased between 1910 and 1920.

Logan is the county seat of Harrison County, which was established on January 15, 1851. Harrison County was named for William Henry Harrison (1773-1841), the ninth President of the United States. In 1853, a site named Magnolia was chosen as the county seat. in 1876, the site was moved to the town of Logan, which was named for General John A. Logan (1826-1886), who had worked to establish Memorial Day. Harrison County received the highest number of Carnegie grants with Logan, Missouri Valley, Dunlap, and Woodbine as recipients.

(Source: Pratt, LeRoy G. “The Counties and Courthouses of Iowa.” Mason City, Ia; Klipto Printing & Office Supply Company, 1977, p. 150.)