East Merrimack is a census-designated place (CDP) in the town of Merrimack, Hillsborough County, New Hampshire, United States. There is no village center named “East Merrimack”; rather, the CDP refers to the region of the town of Merrimack lying east of the F. E. Everett Turnpike, overlapping portions of the villages of Reeds Ferry, Thornton’s Ferry, and the middle of Merrimack. The population was 5,176 at the 2020 census, up from 4,197 at the 2010 census.

East Merrimack is located in the eastern part of the town of Merrimack, bordered to the west by the Everett Turnpike and to the east by the Merrimack River, which forms the town boundary in the same way as Litchfield. To the north, the CDP extends to the Bedford town line, and to the south it extends afterward Star Drive. U.S. Route 3 is the main road through the CDP, leading north 10 miles (16 km) to Manchester and south 7 miles (11 km) to Nashua. The Everett Turnpike is accessible from Exit 11 (Continental Boulevard) near the southern halt of the CDP and from partial Exit 12 (Bedford Road) near the north end.

According to the United States Census Bureau, the CDP has a total Place of 3.7 square miles (9.6 km), of which 3.4 square miles (8.7 km²) are home and 0.3 square miles (0.9 km), or 9.27%, are water. Most of the water area is within the Merrimack River.

As of the census of 2010, there were 4,197 people, 1,928 households, and 1,093 families residing in the CDP. There were 2,028 housing units, of which 100, or 4.9%, were vacant. The racial makeup of the CDP was 93.2% white, 1.3% African American, 0.4% Native American, 1.9% Asian, 0.02% Pacific Islander, 1.1% some extra race, and 2.1% from two or more races. 3.5% of the population were Hispanic or Latino of any race.