Nanostructured surfaces have proven to be effective in controlling the electric field distribution and triggering a series of interesting physical effects. In particular, ordered metallic lattices with a typical size of the same order of magnitude of the wavelength of the incident radiation exhibit extraordinary transmission and reflection properties and represent a sensitive tool to exploit surface plasmon resonance for sensing applications. We investigated, either by experimental structural and optical measurements or by modeling and calculations, samples consisting of a two-dimensional array of polymeric pillars embedded in a gold film. In particular, we analyzed the dependence of the plasmonic resonance on the pillar size. We showed that a peculiar interplay among localized modes and propagating surface plasmon polaritons exists for some selected conditions and affects the spectral distribution, lifetime, and field configuration of the plasmonic excitations.