Dennis is an unincorporated community and census-designated place (CDP) in Delaware County, Oklahoma, near Grand Lake.

Dennis is located in north-central Delaware County on the south side of Grand Lake.

According to the United States Census Bureau, the Dennis CDP has a total area of 4.5 square miles (11.7 km2), all land.

The racial makeup of the CDP was 87.03% White, 7.57% Native American, and 5.41% from two or more races.

13.0% of all households were made up of individuals, and 6.5% had someone living alone who was 65 years of age or older.