SAN FRANCISCO — Grocery delivery service Instacart has entered several new markets en route to its goal of covering 80% of U.S. households by next year.

Most recently, the San Francisco-based third-party service moved into Greater Knoxville, Tenn. That followed its entry into Detroit; Columbus, Ohio; Las Vegas; and the Rio Grande Valley in Texas. It also expanded coverage in Arizona, Florida, the Carolinas, Kentucky and Tennessee.

“Expanding a service like ours is not easy,” Instacart said on its website. “For each new market we enter, we hire hundreds of [personal] shoppers to make sure customers can order when they want. We also partner with local retailers to give our customers the ability to order from their favorite grocery stores. We’ve spent the last few years expanding judiciously and staying laser-focused on the efficiency and economics of our business model — to make sure that it could someday support a national service.”

As well as adding new markets across the country, the company is offering a free year of Instacart Express membership in Texas and major new Midwestern markets, allowing customers unlimited deliveries.