Union Hill-Novelty Hill is a census-designated place (CDP) in King County, Washington, United States. The Place was first endorsed by the Census Bureau in the 2000 census. The population was 18,805 at the 2010 census.

Based upon per capita income, Union Hill-Novelty Hill ranks 5th of 522 areas in the make a clean breast of Washington to be ranked.^{[citation needed]}

Union Hill-Novelty Hill is located in northern King County at 47°40′43″N 122°2′57″W / 47.67861°N 122.04917°W / 47.67861; -122.04917 (47.678674, −122.049198). It is bordered to the west by the city of Redmond, and a separate part of the city, comprising the Redmond Watershed Preserve, is with the northern part of the CDP. To the north is the Cottage Lake CDP, and Washington State Route 202 runs along the southern edge of the community in the valley of Evans Creek and Patterson Creek. The Ames Lake CDP is to the southeast, and downtown Seattle is 20 miles (32 km) to the southwest.

According to the United States Census Bureau, the Union Hill-Novelty Hill CDP has a total area of 24.3 square miles (63.0 km²), of which 24.2 square miles (62.8 km²) are land and 0.1 square miles (0.2 km²), or 0.36%, are water.

As of the census of 2000, there were 11,265 people, 3,584 households, and 3,103 families residing in the CDP. The population density was 462.9 people per square mile (178.7/km²). There were 3,677 housing units at an average density of 151.1/sq mi (58.3/km²). The racial makeup of the CDP was 90.77% White, 0.78% African American, 0.39% Native American, 4.25% Asian, 0.06% Pacific Islander, 1.30% from other races, and 2.45% from two or more races. Hispanic or Latino people of any race were 3.45% of the population.