Sometime in the summer of 1842, wrote a letter on behalf of his wife, Sarah Phinney Foster, and himself from , New York, to JS in , Illinois. He updated JS on his arrival in , where Sarah was apparently visiting friends, and denounced , who was in New York giving public lectures against JS and the . In a postscript, Foster also informed JS of church members who were moving to Nauvoo, including the family of Joseph and Sally Stacy Murdock, whom Foster had encountered on his journey. Foster explained that while Joseph Murdock wanted to donate money to support the construction of the Nauvoo , his wife would likely oppose giving their money to the church. Foster asked JS to watch for their arrival and consider meeting with Joseph Murdock.

dated the letter 16 July 1842, but that likely was a mistake. According to the letter, it took Foster twenty days to travel from to , where he wrote the letter. On 1 July 1842, Foster had transferred a portion of land in , Illinois, to JS, indicating that he was in Hancock County at that time. Further, JS’s journal states that on 19 July JS accompanied Foster and Henry Kearns to investigate land in the Nauvoo area. Given the amount of time it took to get to DeRuyter, it would have been impossible for Foster to have left Nauvoo after 1 July and reached DeRuyter by 16 July, and it would also have been impossible for him to have written a letter in DeRuyter on 16 July and then be back in Nauvoo by 19 July. Because the letter is postmarked 17 August, and because the Fosters reached on 30 August, it is likely that Foster mistakenly wrote down the previous month when dating the letter and that it was actually written on 16 August. No reply from JS has been located.