Medusa is a community in the Town of Rensselaerville.
According to the United States Census Bureau, the CDP has a total area of 6.9 square miles (17.8 km²), of which, 6.8 square miles (17.6 km²) of it is land and 0.1 square miles (0.2 km²) of it (1.02%) is water.
There were 147 households out of which 33.3% had children under the age of 18 living with them, 59.9% were married couples living together, 4.8% had a female householder with no husband present, and 28.6% were non-families. 21.8% of all households were made up of individuals and 7.5% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.04.
In the CDP the population was spread out with 25.5% under the age of 18, 5.6% from 18 to 24, 25.8% from 25 to 44, 26.9% from 45 to 64, and 16.2% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 105.5 males. For every 100 females age 18 and over, there were 105.9 males.
The median income for a household in the CDP was $44,688, and the median income for a family was $50,000. Males had a median income of $35,833 versus $28,750 for females. The per capita income for the CDP was $19,716. About 4.6% of families and 6.7% of the population were below the poverty line, including 10.4% of those under age 18 and none of those age 65 or over.