Marietta, OH has a population of 13,912 and is the 3,007th largest city in the United States. The population density is 1,650 per sq mi which is 541% higher than the Ohio average and 1722% higher than the national average. The median age in Marietta is 38 which is approximately 5% lower than the Ohio average of 39. In Marietta, 49% of the population over 15 years of age are married, 96% speak English and 2% speak Spanish. 65% of Marietta residents were born in Ohio, 32% were born out of state, 1% were born outside of the United States and 2% were foreign born.