Thermoplastic starch compositions that include a particulate filler, e.g. an inorganic filler component, and optional fibrous component The compositions include a thermoplastic phase comprising a thermoplastic starch melt that contains, at a minimum, starch blended with an appropriate plasticizing agent under conditions in order for the starch to form a thermoplastic melt. The thermoplastic phase may also include one or more additional thermoplastic polymers and other optional reactants, liquids or cross-linking agents to improve the water-resistance, strength, and/or other mechanical properties of the thermoplastic melt, particularly upon solidification. The inorganic filler component may affect the mechanical properties but will mainly be added to reduce the cost of the thermoplastic starch compositions by displacing a significant portion of the more expensive starch or starch/polymer melt. Fibers may optionally be included in order to improve the mechanical properties of the thermoplastic starch compositions. The thermoplastic starch compositions may be shaped into a wide variety of useful articles, such as sheets, films, containers, and packaging materials. Because the thermoplastic starch compositions will typically include a thermoplastic phase that is biodegradable, and because the other components will either constitute a naturally occurring mineral and optionally a natural fiber, the overall composition will typically be more environmentally friendly compared to conventional thermoplastic materials.