When he returned to Lynn it was alleged that he made treasonous remarks in the Anchor Tavern against King Charles II of England who was to be crowned on April 23, 1661.
During his hearing on April 1, 1661,[b] he was accused by Nicholas Pinion of saying that "if he hade the King heir, he wold cutte off his head and make a football of it" and by Thomas Tower of saying "I should rather that his head were as his father's rather than he should come to England to set up popery there," an allusion to the 1649 beheading of Charles I.
After seven weeks in prison, on May 22, 1661, the General Court of Massachusetts Bay Colony ruled in Jenckes's favor, citing his subsequent statement supporting the king.
[6][7][2][8][9] The decision was recorded as follows: Joseph Jencks, Juñ, being accused & bound ouer to this Court for high misdemeanor in diuers treasonable words agt the kings majty, wch, vpon examination, he vtterly disounes, neither doeth it appeare that the same cann be legally prooved ast him, only in part, for wch he presenteth & pleadeth the kings gracious act of indempnity, this Court therefore dischardgeth him from his imprisonm̃t.
[2][11] In 1671, he moved to Pawtucket—then northern Providence—where he erected a forge and sawmill on the west side of present-day Blackstone River at Pawtucket Falls.
[12][13][14] Jenckes's Pawtucket forge and home were burned down in 1676 during King Philip's War, which was the first major conflict between Native Americans and New England colonists.
When Jenckes arrived in rural northern Providence, several settlers including Ezekiel Holliman, Thomas Estance, John Smith, Gregory Dextor, Stukely Westcott, and Abel Potter owned land while Richard Scott and Daniel Comstack had built homes.
But it was not until Jenckes built his forge and sawmill at the falls that this sparsely populated area become a village and eventually a center for metalworks and other trades.
[14] Jenckes built his home and forge on the south side of today's Main Street at East Avenue in Pawtucket.
The site of Jenckes's home is marked by a plaque on the Pawtucket Boys Club Building at 53 East Avenue.
[16][17] Jenckes was made a freeman (voting citizen) of the Colony of Rhode Island and Providence Plantations in 1677.
They informed the new monarchs that Sir Edmund Andros, the Governor of the Dominion of New England, had been arrested in the colony after a revolt against him in Boston.
Several of his children had distinguished careers: Joseph was the 19th governor of the Colony of Rhode Island and Providence Plantations, Ebenezer was an ordained minister at the First Baptist Church, and William was a judge and assemblyman.