The seasonal variation of bacterial populations in the Korean cattle (Hanwoo) feedlots dispersed in the 20 cities of Gyeongsangbuk-do, Korea, was monitored for two years (2006 and 2007) to provide quantitative criteria for good agricultural management. Outside the feedlots, the average falling bacterial populations of the air were $3{pm}1$ CFU/$cm^2cdot15$ min (n=63) in a year. Inside the feedlots, the average falling bacterial populations of the air were $8{pm}1$ CFU/$cm^2cdot15$ min (n=63) in the spring, $16{pm}2$ CFU/$cm^2cdot15$ min (n=69) in the summer, $7{pm}2$ CFU/$cm^2cdot15$ min (n=69) in the autumn, and $6{pm}1$ CFU/$cm^2cdot15$ min (n=70) in the winter. Without using the summer data, the average falling bacterial population of the air was $7{pm}1$ CFU/$cm^2cdot15$ min, which was not statistically significant (P=0.37). The average bacterial populations in the cattle drinking water of the cattle feedlots were $4,710{pm}780$ CFU/ml (n=65) in the spring, $10,430{pm}1170$ CFU/ml (n=65) in the summer, $4,820{pm}700$ CFU/ml (n=64) in the autumn, and $2,510{pm}530$ CFU/ml (n=64) in the winter. Without using the summer data, the average bacterial population of the drinking water was $4,000{pm}400$ CFU/ml, which was statistically significant (P=0.027). The average frequency of Escherichia coli O157 inside the feedlots was 5% (n=65) in the spring, 72% (n=65) in the summer, 67% (n=66) in the autumn, and 29% (n=66) in the winter on the basis of soil samples of the year 2007. The results indicate that most of the Escherichia coli O157 strains distributed in the summer and autumn was disappeared in the spring through the cold weather of the winter.