The nests of nine Texas seaside sparrows (Ammodramus maritimus sennetti) collected from a mixed mangrove marsh on Mustang Island, Texas, were examined to determine details of the architecture and placement of nests. Nests were somewhat larger than those described for other seaside sparrow subspecies and were found higher off the ground. They were composed of woven dried grass and typically lacked a canopy. Placement of nests within the marsh seemed to be driven by proximity to the appropriate types of nesting materials in sufficient quantities.