He moved to Minneapolis, Minnesota around 1875.
In May of 1925, he was convicted in federal court of violating the National Prohibition (Volstead) Act and sentenced to a year in jail. During his appeal process, he was re-elected to the Senate. On January 13, 1927, a Senate resolution was offered, which requested that he withdraw from Senate participation during his appeal process. This resolution was referred to the elections committee, which voted 7 to 5 to take no action while the appeal was pending. There were several letters and petitions received by the Senate from the public to either unseat or expel Sen. Lennon throughout the 1927 session. In June of 1927, he was sentenced on appeal to serve a year in jail. On May 12, 1928, he was pardoned by President Coolidge and returned home after serving six and a half months in jail. On January 8, 1929, there was an unsuccessful attempt by the Senate to expel him. The motion did not prevail with 25 yeas and 38 nays.
His funeral services were at St. Anthony of Padua church in Minneapolis.
Religion provided by obituary (Minneapolis Journal, April 26, 1937, p 2); he was a member of the Catholic Order of Foresters and the Holy Name Society.