Trump said he had replaced Tillerson with Central Intelligence Agency Director Mike Pompeo, and had tapped Gina Haspel to lead the CIA.
Futures had gained about 0.4 per cent after U.S. consumer prices data cooled worries about faster U.S. interest rate hikes.
At 8:52 a.m. ET, Dow e-minis 1YMc1 were up 76 points, or 0.3 percent, with 16,110 contracts changing hands.
S&P 500 e-minis ESc1 were up 9.5 points, or 0.34 percent, with 179,598 contracts traded.
Nasdaq 100 e-minis NQc1 were up 24.5 points, or 0.34 percent, on volume of 20,785 contracts.