The numbers below will lead you to the US county data for Agricultural Chemicals, Livestock, Herbicide Use, and Crops. (see http://water.usgs.gov/lookup/listgistheme for available datasets)
Agchem
CA0772 Commercial fertilizer, 1987 (acres)
PCT0772 Percent of county treated with commercial fertilizer, 1987
CA0773 Commercial fertilizer, 1982 (acres)
PCT0773 Percent of county treated with commercial fertilizer, 1982
CA0776 Cropland fertilized, 1987 (acres)
PCT0776 Percent of county as cropland fertilized, 1987
CA0777 Cropland fertilized, 1982 (acres)
PCT0777 Percent of county as cropland fertilized, 1982
CA0780 Pastureland and rangeland fertilized, 1987 (acres)
PCT0780 Percent of county as pastureland and rangeland fertilized, 1987
CA0784 Lime, 1987 (acres on which used)
PCT0784 Percent of county treated with lime, 1987
CA0786 Lime, 1987 (tons)
CA0790 Chemicals used to control insects on hay and other crops, 1987 (acres)
PCT0790 Percent of county treated to control insects on hay and other crops, 1987
CA0791 Chemicals used to control insects on hay and other crops, 1982 (acres)
PCT0791 Percent of county treated to control insects on hay and other crops, 1982
CA0794 Chemicals used to control nematodes in crops, 1987 (acres)
PCT0794 Percent of county treated to control nematodes in crops, 1987
CA0795 Chemicals used to control nematodes in crops, 1982 (acres)
PCT0795 Percent of county treated to control nematodes in crops, 1982
CA0798 Chemicals used to control diseases in crops and orchards, 1987 (acres)
PCT0798 Percent of county treated to control diseases in crops and orchards, 1987
CA0799 Chemicals used to control diseases in crops and orchards, 1982 (acres)
PCT0799 Percent of county treated to control diseases in crops and orchards, 1982
CA0802 Chemicals used to control weeds or grasses in crops, 1987 (acres)
PCT0802 Percent of county treated to control weeds or grasses in crops, 1987
CA0803 Chemicals used to control weeds or grasses in crops, 1982 (acres)
PCT0803 Percent of county treated to control weeds or grasses in crops, 1982
CA0806 Chemicals used for defoliation or growth control in crops, 1987 (acres)
PCT0806 Percent of county treated for defoliation or growth control in crops, 1987
CA0807 Chemicals used for defoliation or growth control in crops, 1982 (acres)
PCT0807 Percent of county treated for defoliation or growth control in crops, 1982
Stock
CA0930 Cattle and calves, 1987 (number)
CA0966 Beef cows, 1987 (number)
CA0984 Milk cows, 1987 (number)
CA1006 Steers, steer calves, bulls, and bull calves, 1987 (number)
CA1094 Hogs and pigs, 1987 (number)
CA1183 Sheep and lambs, inventory, 1987 (number)
CA1210 Horses and ponies, inventory, 1987 (number)
CA1218 Any poultry, 1987 (farms)
CA1222 Chickens 3 months old or older, 1987 (number)
CA1226 Hens and pullets of laying age, 1987 (number)
CA1247 Broilers and other meat-type chickens, 1987 (number)
CA1251 Turkeys, 1987 (number)
CA1261 Any poultry sold, 1987 ($1,000)
Herb
H1980.ACR Acres treated with atrazine
H1980.LBS pounds of atrazine used
H1980.USE rate of atrazine use in county polygon in pounds per square mile
H1863.ACR acres treated with alachlor
H1863.LBS pounds of alachlor used
H1863.USE rate of alachlor use in county polygon in pounds per square mile
H1011.ACR acres treated with metolachlor
H1011.LBS pounds of metolachlor used
H1011.USE rate of metolachlor use in county polygon in pounds per square mile
H1414.ACR acres treated with EPTC
H1414.LBS pounds of EPTC used
H1414.USE rate of EPTC use in county polygon in pounds per square mile
H1302.ACR acres treated with 2,4-D
H1302.LBS pounds of 2,4-D used
H1302.USE rate of 2,4-D use in county polygon in pounds per square mile
H1361.ACR acres treated with trifluralin
H1361.LBS pounds of trifluralin used
H1361.USE rate of trifluralin use in county polygon in pounds per square mile
H1369.ACR acres treated with cyanazine
H1369.LBS pounds of cyanazine used
H1369.USE rate of cyanazine use in county polygon in pounds per square mile
H1839.ACR acres treated with butylate
H1839.LBS pounds of butylate used
H1839.USE rate of butylate use in county polygon in pounds per square mile
H1629.ACR acres treated with pendimethalin
H1629.LBS pounds of pendimethalin used
H1629.USE rate of pendimethalin use in county polygon in pounds per square mile
H1099.ACR acres treated with glyphosate
H1099.LBS pounds of glyphosate used
H1099.USE rate of glyphosate use in county polygon in pounds per square mile
H1298.ACR acres treated with dicamba
H1298.LBS pounds of dicamba used
H1298.USE rate of dicamba use in county polygon in pounds per square mile
H1287.ACR acres treated with bentazon
H1287.LBS pounds of bentazon used
H1287.USE rate of bentazon use in county polygon in pounds per square mile
H1282.ACR acres treated with propanil
H1282.LBS pounds of propanil used
H1282.USE rate of propanil use in county polygon in pounds per square mile
H1124.ACR acres treated with MSMA
H1124.LBS pounds of MSMA used
H1124.USE rate of MSMA use in county polygon in pounds per square mile
H1975.ACR acres treated with metribuzin
H1975.LBS pounds of metribuzin used
H1975.USE rate of metribuzin use in county polygon in pounds per square mile
H1417.ACR acres treated with molinate
H1417.LBS pounds of molinate used
H1417.USE rate of molinate use in county polygon in pounds per square mile
H1305.ACR acres treated with MCPA
H1305.LBS pounds of MCPA used
H1305.USE rate of MCPA use in county polygon in pounds per square mile
H1979.ACR acres treated with propazine
H1979.LBS pounds of propazine used
Crop1
CA2107 Corn for grain or seed, harvested, 1987 (acres)
PCT2107 Percent of county as corn for grain or seed, harvested, 1987
CA2110 Corn for grain or seed, irrigated, 1987 (acres)
CA2117 Sorghum for grain or seed, harvested, 1987 (acres)
PCT2117 Percent of county as sorghum for grain or seed, harvested, 1987
CA2120 Sorghum for grain or seed, irrigated, 1987 (acres)
CA2127 Wheat for grain, harvested, 1987 (acres)
PCT2127 Percent of county as wheat for grain, harvested, 1987
CA2130 Wheat for grain, irrigated, 1987 (acres)
CA2137 Barley for grain, harvested, 1987 (acres)
CA2140 Barley for grain, irrigated, 1987 (acres)
CA2197 Oats for grain, harvested, 1987 (acres)
CA2200 Oats for grain, irrigated, 1987 (acres)
CA2227 Rice, harvested, 1987 (acres)
CA2230 Rice, irrigated, 1987 (acres)
CA2237 Rye for grain, harvested, 1987 (acres)
CA2240 Rye for grain, irrigated, 1987 (acres)
CA2287 Cotton, harvested, 1987 (acres)
CA2290 Cotton, irrigated, 1987 (acres)
CA2297 Tobacco, harvested, 1987 (acres)
CA2300 Tobacco, irrigated, 1987 (acres)
CA2307 Soybeans for beans, harvested, 1987 (acres)
PCT2307 Percent of county as soybeans for beans, harvested, 1987
CA2310 Soybeans for beans, irrigated, 1987 (acres)
CA2317 Dry edible beans, excluding limas, harvested, 1987 (acres)
CA2320 Dry edible beans, irrigated, 1987 (acres)
CA2367 Irish potatoes, harvested, 1987 (acres)
CA2370 Irish potatoes, irrigated, 1987 (acres)
CA2397 Sugar beets for sugar, harvested, 1987 (acres)
CA2400 Sugar beets for sugar, irrigated, 1987 (acres)
CA2427 Sugar cane for sugar, harvested, 1987 (acres)
CA2430 Sugar cane for sugar, irrigated, 1987 (acres)
Crop2
CA2447 Peanuts for nuts, harvested, 1987 (acres)
CA2450 Peanuts for nuts, irrigated, 1987 (acres)
CA2717 Hay--all, harvested, 1987 (acres)
PCT2717 Percent of county as hay--all, harvested, 1987
CA2720 Hay--all, irrigated, 1987 (acres)
CA2727 Alfalfa hay, harvested, 1987 (acres)
CA2730 Alfalfa hay, irrigated, 1987 (acres)
CA2777 Corn for silage or green chop, harvested, 1987 (acres)
CA2780 Corn for silage or green chop, irrigated, 1987 (acres)
CA2807 Land used for vegetables, harvested, 1987 (acres)
PCT2807 Percent of county as land used for vegetables, harvested, 1987
CA2809 Land used for vegetables, irrigated, 1987 (acres)
CA3007 Garlic, harvested, 1987 (acres)
CA3087 Hot peppers, harvested, 1987 (acres)
CA3159 Sweet corn, harvested, 1987 (acres)
CA3167 Tomatoes, harvested, 1987 (acres)
CA3169 Tomatoes, irrigated, 1987 (acres)
CA3232 Apples, total, 1987 (acres)
CA3331 Grapes, total, 1987 (acres)
CA3367 Nectarines, total, 1987 (acres)
CA3403 Peaches, total, 1987 (acres)
CA3457 All citrus fruits, total, 1987 (acres)
PCT3457 Percent of county as all citrus fruit, total, 1987
CA3484 Lemons, total, 1987 (acres)
CA3493 Limes, total, 1987 (acres)
CA3502 Oranges, total, 1987 (acres)
CA3619 Berries, harvested, 1987 (acres)
CA3810 Sod, harvested, 1987 (acres)
CA3814 Sod, harvested, 1982 (acres)