Greentown was incorporated some time between 1870 and 1880 as it first appeared on the US census in 1880. The population started out at just over 200, and quickly reached a thousand. Over the years since, Greentown's population numbers have seen notable gains every couple censuses followed by smaller drops between, which has enabled the town to slowly grow over time. The population has remained at nearly 2,500 since the 1990s. Greentown is expected to annex more area when the sewage treatment plant is updated, which is expected to bring another gain soon.