Dover Downs has announced "over 99%" of votes were cast in favour of the merger, with the subsequent transaction expected to be closed on 28 March.
Completion of the merger will see Dover Downs become a wholly owned subsidiary of Twin River.
The casino is the second-best performing of three sports betting locations in Delaware, accepting $3.1m in sports wagering handle in December and $2.1m in January.
Twin River, meanwhile, runs two casinos in Rhode Island, one in Mississippi and a horseracing track in Colorado.
Bettors in Rhode Island will soon be able to place online and mobile sports wagers via Twin River’s sportsbook, after Governor Gina Raimondo approved a bill legalising mobile sports betting.
