An investigation of the proton ground-state configurations in the even zirconium isotopes (A = 90, 92, 94, 96) was undertaken using the (d, 3 He) reaction at a deuteron energy of 34.4 MeV. The experimental angular distributions were compared with distorted-wave calculations in the finite-range approximation which include nonlocality in the distorted waves. The residual yttrium isotopes (A =89, 91, 93, 95) have £~* ground states, and the observed spectra can be interpreted in terms of a simple shell-model picture which considers hole and particle configurations in the lg 9 /2, 2pi/2, 2p 3/2 , and l/ 5 / 2 proton shells and allowed couplings in the 2^5/2 neutron shell. It was found that the filling of the 2d 5 /2 neutron shell apparently has a measurable effect on the relative amounts of the (2^i /2 ) 2 and (lgg/ 2 ) 2 proton admixtures in the zirconium ground states. The strength of the (2^i/ 2 ) 2 term in the ground-state wave functions was determined to be: 64% for 90 Zr, 55% for 92 Zr, 66% for ^Zr, and 86% for 96 Zr.