In the Kentucky Constitution there is a 6 year residency requirement. There is also an official procedure for protesting the eligibility of a candidate. Virginia Woodward, Democrat, Louisville, filed a motion before the November 2 election after she heard that Ms. Seum Stephenson, Republican, New Albany, Indiana, had lived in Indiana for most of the time since 1997, when she move to southern Indiana to attend IUS for in-state tuition. Seum Stephenson beat Woodward by 1,000 votes in blue collar southern Metro Louisville. She was ruled ineligible by a judge.
Today Seum Stephenson was seated as the State Senator by the Republican-controlled Senate, overriding the Kentucky Constitution, the Judge who declared her ineligible, and even a Senate subcommittee who recommended the post to Woodward. A Republican Senator who had proposed a special election be held is resigning his seat in protest. I'll edit this later with some links, but information is available on changeforkentucky.com and DFA.