We calculate the strange quark content of the nucleon < N vertical bar(s) over bars vertical bar > in 2 + 1 -flavor lattice QCD. Chirally symmetric overlap fermion formulation is used to avoid the contamination from up and down quark contents due to an operator mixing between strange and light scalar operators, (s) over bars and (u) over baru + (d) over bard. At a lattice spacing a = 0.112(1) fm, we perform calculations at four values of degenerate up and down quark masses m(ud), which cover a range of the pion mass M-pi similar or equal to 300-540 MeV. We employ two different methods to calculate < N vertical bar(s) over bars vertical bar >. One is a direct method where we calculate < N vertical bar(s) over bars vertical bar > i by directly inserting the (s) over bars operator. The other is an indirect method where < N vertical bar(s) over bars vertical bar > is extracted from a derivative of the nucleon mass in terms of the strange quark mass. With these two methods we obtain consistent results for < N vertical bar(s) over bars vertical bar > with each other. Our best estimate f(Ts) = m(s)< N vertical bar(s) over bars vertical bar >/M-N = 0.009(15)(stat)(16)(sys) is in good agreement with our previous studies in two-flavor QCD. DOI: 10.1103/PhysRevD. 87.034509