Chelsea is a city in Suffolk County, Massachusetts, United States, directly across the Mystic River from the city of Boston. It is the smallest city in Massachusetts in land area, and the 26th most densely populated in the country. As of the 2010 Census, it had a population of 35,177. According to the United States Census Bureau, Chelsea has a total area ofBad rounding here{{#invoke:Math|precision_format| 6.4*1,000,000/2,589,988.110336 | 1-0 }} square miles (6.4 km), of whichBad rounding here{{#invoke:Math|precision_format| 5.7*1,000,000/2,589,988.110336 | 1-0 }} square miles (5.7 km) is land andBad rounding here{{#invoke:Math|precision_format| 0.6*1,000,000/2,589,988.110336 | 1--1 }} square miles (0.6 km), or 10.02%, is water. Located on a peninsula in Boston Harbor, Chelsea is drained by Chelsea Creek and sits on the Mystic River just north of downtown Boston.