We demonstrate automatic design of infrared (IR) metamaterials using a genetic algorithm (GA) and experimentally characterize their IR properties. To implement the automated design scheme of the metamaterial structures, we adopt a digital metamaterial consisting of 7 × 7 Au nano-pixels with an area of 200 nm × 200 nm, and their placements are coded as binary genes in the GA optimization process. The GA combined with three-dimensional (3D) finite element method (FEM) simulation is developed and applied to automatically construct a digital metamaterial to exhibit pronounced plasmonic resonances at the target IR frequencies. Based on the numerical results, the metamaterials are fabricated on a Si substrate over an area of 1 mm × 1 mm by using an EB lithography, Cr/Au (2/20 nm) depositions, and liftoff process. In the FT-IR measurement, pronounced plasmonic responses of each metamaterial are clearly observed near the targeted frequencies, although the synthesized pixel arrangements of the metamaterials are seemingly random. The corresponding numerical simulations reveal the important resonant behavior of each pixel and their hybridized systems. Our approach is fully computer-aided without artificial manipulation, thus paving the way toward the novel device design for next-generation plasmonic device applications.