Political parties use the internet, and social media in particular, for fundraising, advertising, and mobilizing to achieve desirable ends. Local parties are first and foremost organizations, and so as they make their decisions, they have to use their resources wisely. Through our analysis of over 6000 county-level Democratic and Republican parties in the United States, we find a high degree of variation in the use of social media platforms (Facebook, Twitter, and Instagram) by parties. In explaining this variation, we focus on parties as organizations and so find the choice to use social media and their overall activity on it reflects the resources available to the party organization, as well as the size of potential audience and the competitiveness of their political environment. Although these variables explain local Democratic parties better than they explain local Republican parties.