Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or lightly grease it.
In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth.
Add the egg and vanilla extract to the butter mixture. Mix until well combined.
In another bowl, whisk together the rolled oats, flour, baking soda, cinnamon, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in the raisins until evenly distributed throughout the dough.
Using a tablespoon or cookie scoop, drop the dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden.
Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.