A method is described for the in situ growth of substrate-supported organized gold nanoparticles. Upon exposure to an aqueous solution of a gold salt and a mild reducing agent, the particle size can be significantly increased without any loss of superstructure organization. Furthermore, no secondary nucleation is observed. The surface-supported regrowth procedure can be combined with the Langmuir-Blodgett technique to produce a rich library of plasmonic nanoparticle assemblies. Controlled particle regrowth plays a crucial role in this assembly method because only relatively small metallic nanoparticles can be directly dispersed in polymeric Langmuir-Blodgett films. The versatility of the method is demonstrated through the fabrication of several specific nanoparticle structures, including contiguous plasmonic rings, core-satellite structures, and necklace assemblies. Plasmon extinction spectra are presented for the various nanoparticle superstructures and illustrate the importance of controlling both particle size and assembly architecture in achieving targeted optical properties. The reported approach constitutes a viable bottom-up assembly route for the fabrication of surface-supported nanoparticle superstructures for plasmonic applications.