https://foreignpolicy.com/2020/10/27/election-cybersecurity-cyberattack-critical-infrastructure-voting/
"Voting Machine Manufacturers: Critical Players in Safeguarding Election Integrity
Three private companies, Election Systems & Software (“ES&S”), Dominion Voting Systems (“Dominion”) and Hart InterCivic (“Hart”) manufacture and manage the vast majority of U.S. electronic voting machines, controlling 84.08 percent of total eligible voter population. ES&S is the largest vendor, holding 37.97 percent of the market share by precinct and servicing more than 90.31 million registered voters. Followed by Dominion who controls 35.14 percent by precinct and Hart with 10.97 percent by precinct."
but i'd recommend this site for more information and the interactive version of that map:
https://verifiedvoting.org/verifier/#mode/navigate/map/ppEquip/mapType/normal/year/2020