I left out the fact that Joseph of the Matawasca area had a wife and three children under five in 1830, meaning this man, if he was the same one, may have married around 1825. That Joseph was between 20 and 30 years old in 1830. Joseph Fournier of Illinois in 1850 was 50 that year. Mary Octavia was not born until 1833 to 1836.
Also, they apparently lived in the section of land that changed countries, which appears to be what your book covers. In 1840 Joseph and some of his neighbors appeared in the Maine, U.S., census without having moved. But by 1850 they'd all vanished back to Canada, again without moving.