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is a city in McPherson County, South Dakota, United States. The population was 1,101 at the 2000 census.
According to the United States Census Bureau, the city has a total area of 1.0 square miles (2.6 km²), of which, 0.9 square miles (2.4 km²) of it is land and 0.1 square miles (0.2 km²) of it (7.00%) is water.
Eureka has been assigned the ZIP code 57437 and the FIPS place code 20180.