Corn fields in Ohio were surveyed in 2013 and 2014 to determine the frequency and abundance of plant-parasitic nematodes. Soil samples were collected at a depth of 40 to 50 cm from 425 fields when corn was between growth stages V3 and V6. A total of 15-16 fields were sampled in each of 28 counties, across 6 soil regions, representing three cropping systems and three tillage programs. Standard laboratory techniques were used for processing and extraction, and plant-parasitic nematodes were identified to genus. Nine commonly occurring morphological groups of plant-parasitic nematodes, namely spiral (Helicotylenchus spp.), lesion (Pratylenchus spp.), lance (Hoplolaimus spp.), dagger (Xiphinema spp.), stunt (Tylenchorhynchus spp.), pin (Paratylenchus spp.), ring (Criconemella spp.), stubby-root (Paratrichodorus spp.), and cyst (Heterodera spp.), along with several genera in the subfamily Tylenchinae counted together as “tylenchids”, were identified, with maximum individual-field population densities ranging from 26 to 1,164 nematodes/100 cm3 soil, depending on the group. Generalized linear mixed models were fitted to the data to estimate county-level heterogeneity in nematode presence, while binary and ordinal logistic regression models were fitted to estimate the odds of each genus being present, and the lesion, lance, spiral, and pin nematodes at potentially damaging population densities based on soil region, cropping sequence, tillage, and soil pH, silt content, and electrical conductivity. The spiral nematodes and tylenchids were detected in 94 and 96% of the fields, whereas the lesion, pin, lance, stunt, and dagger nematodes were recovered from 80, 57, 48, 48, and 37% of the fields, respectively. The stubby-root, cyst, and ring nematodes were the least frequent, each identified from fewer than 13% of the fields. County-level heterogeneity varied among the genera, with variance estimates ranging from 0.56 to 3.23. However, except for comparisons between the stunt and pin, stunt and dagger, and lance and dagger nematodes, the 95% confidence intervals around the variance estimates overlapped considerably, suggesting comparable county-level heterogeneity across genera. Based on odds ratios, all covariates affected nematode populations, but soil region had the greatest and most consistent effect. Dagger and ring nematodes were more likely to be present in region 6 than any of the other regions, but lance, stunt, pin, stubby-root, and spiral nematodes were more likely to be present in regions 1, 2, 3, 4, and 5 than 6. The odds of spiral, lance, and pin nematode population densities being at moderate to high levels in region 3 and 4 were greater than the odds in region 6, but region 1 was more likely than 6 to have lance nematode population densities at high risk levels. The spiral nematode was also likely to reach higher risk levels in regions 1, 2, and 5 than 6, and pin nematode was more likely to reach high risk levels in region 2 than 6. Spiral, lance, and pin nematode were more likely to be present in fields under corn-soybean or corn-soybean-wheat rotation than under continuous corn, and the odds of the pin nematode population density being at moderate to very severe risk levels were two times greater for field under rotation than fields under continuous corn. Tillage was associated with the presence of lance, stubby-root, and stunt nematode, with the former two genera being more likely to be found in fields under conservation tillage than conventional tillage, while the opposite was true for the latter genus. The lance nematode was also more likely to reach yield-impacting population densities in conservation than conventional tillage fields. As soil pH increased, the probability of the spiral nematode population densities being in the moderate to very severe risk category increased, but the probability of the lesion and pin nematode population densities being in that same risk category decreased. For the lesion and lance nematodes, the probability of population densities being in the moderate to very severe risk category decreased as the silt content of the soil increased. Soil electrical conductivity had contrasting effects on the probability of lesion and pin nematode population densities reaching high-risk levels.