This supplement contains extra material related to our study of the Great Reform Act. Appendix S1 lists definitions and sources of all the variables used in the analysis. Appendix S2 explains how the variable Connection to London is constructed. Appendix S3 contains a discussion of the placebo tests. Appendix S4 contains a discussion of alternative explanations for the Whig victory in 1831. All the supplementary tables (S1 to S28) and the maps (S1 and S2) are collected at the end of the appendix. Tables S26 to S28 report summary statistics for the variables used in supplementary tests.