Embodiments of a cutting insert are provided. The cutting insert includes an upper surface, a lower surface, a plurality of side surfaces extending between the upper surface and the lower surface, an insert hole extending through the upper surface and the lower surface, and a corner portion provided with a cutting edge. At least one of the upper surface and the lower surface has a plurality of recesses extending between the insert hole and the corner portion. The plurality of recesses includes a first recess into which one portion of the mounting portion is inserted when the cutting insert is supported by the mounting portion, and a second recess into which another portion of the mounting portion is inserted when the cutting insert is supported by the mounting portion. The second recess has a side wall spaced apart from another portion of the mounting portion.