The United States provides a unique laboratory for understanding how the cultural, institutional, and human capital endowments of immigrant groups shape economic outcomes. In this paper, we use census micro-sample information to reconstruct the country-of-ancestry distribution for US counties from 1850 to 2010. We also develop a county-level measure of GDP per capita over the same period. Using this novel panel data set, we investigate whether changes in the ancestry composition of a county matter for local economic development and the channels through which the cultural, institutional, and educational legacy of the country of origin affects economic outcomes in the US. Our results show that the evolution of the country-of-origin composition of a county matters. Moreover, the culture, institutions, and human capital that the immigrant groups brought with them and pass on to their children are positively associated with local development in the US. Among these factors, measures of culture that capture attitudes towards cooperation play the most important and robust role. Finally, our results suggest that while fractionalization of ancestry groups is positively related with county GDP, fractionalization in attributes such as trust, is negatively related to local economic performance.