The present invention provides modular and distributed methods and systems to convert biomass feedstocks into synthesis gas (syngas). The syngas can then be turned into liquid chemicals and fuels such as ethanol. The modular units of the invention bring the conversion process to the biomass source, thereby minimizing feedstock transportation costs. The modules are capable of being connected to, and/or disconnected from, each other to easily adjust the overall feedstock capacity. The present invention also provides methods and systems to determine an optimal number and distribution of modular conversion units spatially located within a region of land. The disclosed methods and systems are flexible, efficient, scalable, and are capable of being cost-effective at any commercial scale of operation.