A comprehensive WI state-wide assessment of waterhemp response to a diverse group of herbicide sites of action (SOAs) has not been conducted. Our objective was to characterize the response of a WI state-wide collection of waterhemp accessions to postemergence (POST) and preemergence (PRE) herbicides commonly used in corn and soybean. Greenhouse experiments were conducted with more than 80 accessions from 27 counties. POST treatments were 2,4-D, atrazine, dicamba, fomesafen, glufosinate, glyphosate, imazethapyr, and mesotrione at 1× and 3× label rates. PRE treatments were atrazine, fomesafen, mesotrione, metribuzin, and S-metolachlor at 0.5×, 1×, and 3× label rates. Ninety-eight and 88% of the accessions exhibited ≥ 50% plant survival after exposure to imazethapyr and glyphosate POST 3× rate, respectively. Seventeen, 16, and 3% of the accessions exhibited ≥ 50% plant survival after exposure to 2,4-D, atrazine, and dicamba POST 1× rate, respectively. Survival of all accessions was ≤ 25% after exposure to 2,4-D or dicamba POST 3× rate, or glufosinate, fomesafen, and mesotrione POST at either rate evaluated. No plant of any accession survived exposure to glufosinate at either rate. Forty-five and 3% of the accessions exhibited < 90% plant density reduction after exposure to atrazine PRE 3× rate and fomesafen PRE 1× rate, respectively. Plant density reduction of all accessions was ≥ 96% after exposure to fomesafen PRE 3× rate, or metribuzin, S-metolachlor, and mesotrione PRE 1× rate. Our results suggest that waterhemp resistance to imazethapyr and glyphosate POST is widespread in WI, whereas resistance to 2,4-D, atrazine, and dicamba POST is present to a lower extent. One accession (A75, Fond du Lac County) exhibited multiple resistance to imazethapyr, atrazine, glyphosate, and 2,4-D POST. Overall, atrazine PRE was ineffective for waterhemp control in WI. Proactive resistance management and the use of effective PRE and POST herbicides are fundamental for waterhemp management in WI.