Conservation organizations often must rely on data collected quickly and cheaply to make informed decisions in unstudied regions. Butterflies represent an opportunity in this respect, in that many species can typically be sampled and identified in a short time and provide an indication of habitat or conservation value as well. During nine days of sampling in June 2008, we found and identified 84 butterfly species and 1,856 butterfly individuals at Playa El Icacal, Department of La Unión, El Salvador, using transect counts. Through species richness estimators and a ratio extrapolation based on a list of species expected to be found onsite, we sampled 40–60% of the butterfly community present. Species richness at the site is estimated to be between 100 and 200 species. Sites with small patches of dry forest (La Bocana and La Laguna) had higher species richness than sites without dry forest (Hacienda Casco, El Manglar, and El Esteron). While two weeks is not enough time to fully document the butterfly community in 20 km² of neotropical coastal countryside, we were able to provide a valuable estimate of species richness and provide some information as to which areas in the region hold the most conservation value. We suggest using a list of widespread species with modified habitat associations for use as an inventory index for ratio extrapolation and discuss specific guidelines for future butterfly rapid assessments in Mesoamerica.