Kempin started eight times for the Crew in 2018-19 but did not make any appearances in 2020. Instead, he logged 11 starts while on loan to second-flight San Diego. In his career, he has started more than 50 matches in the lower divisions.
His career high in MLS starts was seven in 2017 with the Galaxy.
He will be a prime candidate to start for Loudoun United, D.C.'s second-tier team.
United was in the market for a goalkeeper after free agent Earl Edwards Jr., 28, signed with the New England Revolution last month. With five goalkeepers on its roster, Columbus was eager to make a move before the draft.
The third goalkeeping slot in MLS is often set aside for a young player, who subsequently gains experience in the lower divisions, but United opted for experience.
Simon Lefebvre, United’s first-round draft pick last year, seemed like a candidate after playing last year on a second-division contract for Loudoun United. But D.C. did not offer him an MLS deal this winter, and he signed this week with second-tier Louisville. (United retains his MLS rights.)
In 2010, at age 17, Kempin was Kansas City’s first homegrown signing. He was a member of the U.S. under-18, under-20 and under-23 national teams.
With the trade, United has 21 players under contract and is in negotiations to retain defender Chris Odoi-Atsem and midfielder Felipe Martins. The team is also seeking to acquire a striker to compete with Ola Kamara for playing time, a center back and at least one outside back.
The roster maximum is 30 players.
United owns the No. 4 overall pick in the college draft.
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