Nebraska crop production estimates, based primarily on surveys conducted with farmers and ranchers last fall, are at http://www.nass.usda.gov/Quick_Stats/

The top five corn-producing counties in Nebraska in 2017 were:

1. York (45.4 million bu);
2. Hamilton (42.1 million bu);
3. Antelope (40.5 million bu);
4. Buffalo (39.7 million bu); and 
5. Phelps (38.9 million bu)

The top five soybean-producing counties in Nebraska in 2017 were:

1. Saunders (9,995,000 bu);
2. Gage (8,758,000 bu);
3. Platte (8,472,000 bu);
4. Antelope (8,468,000 bu); and
5. Cuming (7,665,000 bu).

More county-level data is available.