This small collection of Robert Mills family letters date from 1813 to 1847 and measures 0.2 linear feet. Found here are 38 letters between architect Robert Mills and his wife Eliza, the majority of which were written between 1813 and 1819, and generally discuss family news and health, his travels, finances, and their affection for each other. Also found are a fragment of a letter to Mills from his sister, Sarah, a letter to Mills from his mother-in-law, Ann Smith, and nine letters to Mills from business acquaintances, including architect John Skirving and engineer Louis Wernwag, regarding building projects. The collection also includes six letters to Mills' daughter Anna from her mother, Eliza, and cousins.

He executed commissions from Newburyport, Massachusetts, to Mobile, Alabama, and worked in Philadelphia, Baltimore, Columbia, South Carolina, and Washington, D.C.