We present measurements of a topological property, the Chern number ($C_mathrm{1}$), of a closed manifold in the space of two-level system Hamiltonians, where the two-level system is formed from a superconducting qubit. We manipulate the parameters of the Hamiltonian of the superconducting qubit along paths in the manifold and extract $C_mathrm{1}$ from the nonadiabitic response of the qubit. By adjusting the manifold such that a degeneracy in the Hamiltonian passes from inside to outside the manifold, we observe a topological transition $C_mathrm{1} = 1 rightarrow 0$. Our measurement of $C_mathrm{1}$ is quantized to within 2 percent on either side of the transition.
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