[2] It is identified as one of several small communities with a combined population of 24,402 forming the unincorporated town of Aptos by the local Chamber of Commerce along with: For statistical purposes, the United States Census Bureau has defined Seacliff as a census-designated place (CDP).

According to the United States Census Bureau, the CDP covers an area of 0.8 square miles (2.0 km2), 99.90% of it land and 0.10% of it water.

The 2010 United States Census[5] reported that Seacliff had a population of 3,267.

504 households (32.8%) were made up of individuals, and 142 (9.2%) had someone living alone who was 65 years of age or older.

There were 1,923 housing units at an average density of 2,506.1 per square mile (967.6/km2), of which 796 (51.8%) were owner-occupied, and 740 (48.2%) were occupied by renters.