Name Sites Samples
Oktibbeha County 17 65
Oneida County 4 4
Onslow County 13 53
Ontonagon County 1 2
Orange County 2 4
Orange County 2 4
Orange County 4 6
Orange County 2 8
Orange County 6 13
Orange County 1 4
Orleans Parish 7 26
Osage County 1 5
Osage County 12 39
Osceola County 1 4
Otoe County 2 6
Ottawa County 1 1
Ouachita County 1 10
Owen County 1 3
Page County 3 12
Palm Beach County 10 71
Panama 11 51
Panola County 2 28
Paraguay 2 2
Parke County 2 5
Parker County 2 3
Patrick County 3 7
Pawnee County 3 3
Pawnee County 1 2
Pearl River County 1 6
Perry County 3 17