Gronstal and his wife, Connie, have two daughters: Kate, who is a transportation engineer at Stantec in Chicago; and Sara, who is currently Director of Forensics at Eastern Illinois University.

Gronstal was re-elected in 2004 with 12,480 votes (54%), defeating Republican opponent Loren Knauss.

Gronstal also supported legislation to increase funding for community colleges and school districts.

After the Iowa Supreme Court ruled in favor of gay marriage in the Varnum v. Brien decision in April 2009, Gronstal blocked a Republican attempt to overturn the Court's decision with a constitutional amendment.

He released a YouTube video in which he quoted his daughter's statement that opponents of same-sex marriage in Iowa had already lost because her generation does not care about the issue.