NEWTON, Iowa — Two or three days a week, for up to five hours, Liz Mueller plants herself in a coffee shop called Uncle Nancy’s.

She posts to Facebook, makes calls and meets one on one with people over bottomless mugs of flavored black coffee. Her goal is to become known throughout this farming community of 15,000 as “the Hillary girl.”

Ms. Mueller, who at 24 is already a disciplined veteran of political campaigns in Virginia, New York and Arkansas, is one of Hillary Rodham Clinton’s 47 paid organizers in Iowa, a sizable and growing army. The formidable infrastructure, larger than any other candidate’s for either party in Iowa, shows Mrs. Clinton’s determination not to leave anything to chance in the state with the first nominating contest, where she suffered a bruising setback in her last presidential run.

At the same time, her Iowa organization, which some might consider overkill given Mrs. Clinton’s commanding lead in Democratic polls and fund-raising, is also meant to be a boot camp for organizers. The best ones will be in line to lead teams or entire states in the general election if Mrs. Clinton is the Democratic nominee.