Several theories suggest that states’ choices of constitutional rules are at least partially a function of neighboring constitutions. This paper provides the first analysis of spatial dependence of specific provisions within state constitutions in the United States. The analysis effectively makes constitutional rules endogenous, contributing to a relatively underdeveloped branch of constitutional economics. By employing a series of probit estimations of nineteen specific constitutional rules, I find evidence of spatial dependence in state constitutions. Specifically, the presence of specific constitutional constraints pertaining to term limits, supreme court justice selection, recall, home rule, direct democracy, constitutional amendment by convention, balanced budget requirements, tax and expenditure limits, line item veto, victims’ bill of rights, health and welfare, right to privacy, environmental protection, sex discrimination, abortion, and official language all exhibit some evidence spatial dependence.