Landscape fragmentation often increases contact between humans, wildlife, and potential disease vectors. We examined how adult host-seeking mosquitoes respond to small-scale habitat differences within southern Great Plains cross-timber habitat mosaics in northern Oklahoma consisting of eastern red cedar (Juniperus virginianus L.) woodlands, mixed-deciduous woodlands, and adjacent grasslands. Mosquitoes responded most markedly to an overall grassland-woodland habitat gradient, with species separating by habitat based largely on tree density. Differences in abundance of host-seeking females occurred at fine spatial scales, sometimes varying dramatically over distances as little as 200 m when tree density changed abruptly. Tree type was not as important as tree density, although the West Nile virus vector Culex tarsalis Coquillett showed a greater affinity for areas containing eastern red cedar than for deciduous woodlands. The invasive Aedes albopictus Skuse showed equal affinity for both tree types. Conversion of grassland habitats in the Great Plains to more vegetated environments associated with humans (towns and homesteads) and the invasion of grasslands by eastern red cedar may change the species composition of mosquito, bird, and mammal assemblages and potentially alter arbovirus exposure for humans.