Hardin is a city in Liberty County, Texas, United States. Its population was 768 at the 2020 census. According to the United States Census Bureā¦Hardin is a city in Liberty County, Texas, United States. Its population was 768 at the 2020 census. According to the United States Census Bureau, the city has a total area of 2.3 sq mi, all land. As of the 2020 United States census, there were 768 people, 302 households, and 183 families residing in the city.