Allen joined his cousin Remember Baker and his brother Ira, Heman, and Zimri to form the Onion River Company in 1772, a land-speculation organization devoted to purchasing land around the Winooski River, which was known then as the Onion River. The success of this business depended on the defense of the Wentworth grants. Early purchases included about from Edward Burling and his partners; they sold land at a profit to Thomas Chittenden, among others, and their land became the city of Burlington.