Longstanding debates in development economics and economic history have been concerned with the role of the state in supporting economic development. A leading view is that legal capacity – the ability of a state to enforce its laws – plays a key role. But exactly how is legal capacity developed? What are its longer-term effects within economies? We study how local legal capacity developed in England and Wales immediately prior to the Industrial Revolution. Following the 1688-9 Glorious Revolution, Parliament relied on local magistrates, known as Justices of the Peace (JPs), to enforce property rights and administer market regulation. We show that counties with more JPs in 1700 experienced more economic growth – proxied by population density – over the following 140 years. Higher JP numbers are also associated with more industrial development, and greater investment in local infrastructure. We argue, using a simple model, that the number of JPs was constrained by the size of the local gentry. Using the stock of local elites as an instrument for JPs strengthens the causal interpretation of our results.