In 2019, Plummer sponsored legislation that allowed courts to forbid contact between defendants in custody and victims. The legislation passed the legislature and was signed into law by Governor J.B. Pritzker in July 2019. Both the Illinois Sheriffs Association and Illinois Association of Chiefs of Police backed the bill. Another bill sponsored by Plummer, HB 3462, allows Illinois schools to include hunting safety classes as part of the curriculum. Plummer cited expanded hunting safety as one of his chief concerns when sponsoring the bill. The legislation was signed into law and became effective immediately. On the issue of taxes, Plummer supports lowering the state income tax. In early 2019, he cosponsored a proposal which would call for a new amendment to the Illinois state constitution that would require a two-thirds supermajority in both houses of the legislature for any measure that raises taxes or state fees. Plummer was first elected to the Illinois Senate in 2018. In the primary election, he defeated Greenville University basketball coach George Barber, Clinton County Board member Rafael Him, and Marion County Republican Party Chairman Benjamin Stratemeyer in a four way primary winning 57% of the total vote and defeated Democratic nominee Brian Stout in the general election. In April 2020, Plummer called on the federal government to not bail out Illinois, arguing that its fiscal problems came because it "failed to aggressively pay down debt or plan for a rainy day."
Prior to his election as a state senator, Plummer was vice president of R.P. Lumber, one of the largest family-owned hardware, lumber and building material companies in the U.S. The company was founded by Plummer's parents in 1977 and grew from one retail location to 66 locations across Illinois and Missouri. In 2017, the North American Retail Hardware Association selected Plummer from a pool of candidates nationwide to be named the Young Retailer of the Year. Plummer is a partner and senior adviser at Cimbria Capital, a commercial investment firm, and also serves as a director at Cimbria Invest, LLC. Prior to Cimbria Capital, Plummer was on the board of TheBANK of Edwardsville. He also served on the board of directors for several businesses and non-profit organizations. He also served on the board of the Illinois Lumber and Material Dealers Association and was an active member in the Illinois Business Alliance and local chambers of commerce.
