Patterning of materials at single nanometer resolution allows engineering of quantum confinement effects, as these effects are significant at these length scales, and yields direct control over electro‐optical properties. Silicon is by far the most important material in electronics, and the ability to fabricate Si‐based devices of the smallest dimensions for novel device engineering is highly desirable. The work presented here uses aberration‐corrected electron‐beam lithography combined with dry reactive ion etching to achieve both: patterning of 1 nm features and surface and volume plasmon engineering in Si. The nanofabrication technique employed here produces nanowires with a line edge roughness (LER) of 1 nm (3σ). In addition, this work demonstrates tuning of the Si volume plasmon energy by 1.2 eV from the bulk value, which is one order of magnitude higher than previous attempts of volume plasmon engineering using lithographic methods. 1 nm resolution Si patterning is achieved using aberration‐corrected electron‐beam lithography (AC‐EBL) and reactive ion etching, techniques compatible with Si technology processes, resulting in features with a line edge roughness of 1 nm. AC‐EBL is also used to tune the Si volume plasmon energy as a function of nanostructure geometry, demonstrating control of electro‐optical properties of nanostructures “by design.”