This study investigated antimicrobial resistance of 80 Salmonella Typhimurium DT104 strains on 17 commercial swine farms in Ontario. Of the 24 antimicrobials tested, the isolates showed resistance to 4 to 10 of them. Most frequently, the isolates showed resistance to  sulfonamides (Su), ampicillin (A), streptomycin (S), spectinomycin (Sp), chloramphenicol (C), tetracycline (T), and florfenicol (F). Thirteen resistance patterns were observed with 88% of  the isolates presenting with the resistance pattern “ACSpSSuT.” Plasmid profiles were investigated and the isolates were classified into 23 distinct genotypes by PFGE-SpeI 1 BlnI.  In total, 39 distinct “types” were observed when a “type” was based on antimicrobial resistance, plasmid pattern, and PFGE-SpeI 1 BlnI for each isolate. In conclusion, the diversity of isolates discovered suggessts the Salmonella Typhimurium DT104 strains come from multiple sites on the swine farms. These findings can be used to determined the exact source of contamination as well as to trace Salmonella Typhimurium DT104 infections in humans back to the source either swine-related or from other food-producing animals.