If you win in local land-based casinos then yes. The US government requires a 25% tax on gambling winnings of over $600 at a horse track, $1,200 in a slot machine/bingo game, $1,500 in keno winnings, and $5,000 in poker tournaments.
The same tax rules apply for US residents when playing in online casinos, irrespective of where the site is based. Residents can look to offset losses when working out taxes owed but we suggest speaking to a tax specialist to help with this. It can also differ from state to state so where you live can make a big difference in how much tax is payable on winnings.