According to the latest results, released Monday, Tulowitzki leads NL shortstops, and is followed by the Brewers' Jean Segura, the Giants' Brandon Crawford, the Cardinals' Jhonny Peralta, and the Dodgers' Hanley Ramirez.
Castro was named to the All-Star team in 2011 and '12, but last year struggled to bat .245 in 161 games.
"It's one of the biggest goals I have this year," Castro said Monday about making the NL team. "The year I had last year, it would be great for me in my career to make the All-Star team. That's one of my biggest goals, is to make it a good year and to go the All-Star Game. ... I'll keep playing hard, and if it happens, it happens."
Castro was batting .287 with 84 hits, while Tulowitzki is hitting .360 with 89 hits. Castro's 34 extra-base hits are tied for the most in the league with Tulowitzki. Castro, Tulowitzki and the Astro's Jose Altuve are the only three players in the Majors this season with at least 12 games of three or more hits.
On Friday, Castro hit his 11th home run of the season, surpassing his 161-game total of 10 home runs last year.
The other Cubs player with a chance to go to the All-Star Game in Minneapolis on July 15 is Anthony Rizzo, although he has not cracked the top five in the voting for NL first basemen. The D-backs' Paul Goldschmidt leads the field, and is followed by the Dodgers' Adrian Gonzalez, the Braves' Freddie Freeman, the Brewers' Mark Reynolds, and Matt Adams of the Cardinals.
Rizzo has 12 home runs since April 30, tied for second-most in the NL in that span with Goldschmidt and the Marlins' Giancarlo Stanton. The Reds' Todd Frazier leads with 17 homers.
Rizzo has 34 walks, a .408 on-base percentage, and a .955 OPS in his last 47 games dating to April 30, plus nine doubles, 12 homers and 32 RBIs in that stretch. He ranks fifth in the league with a .398 OBP.
No Cubs players were listed among the top vote-getting position players, and the team's representative could be a pitcher. Jeff Samardzija was ninth in the NL with a 2.60 ERA while Jason Hammel was 16th with a 2.99 ERA.
Fans can cast their votes for starters at MLB.com and all 30 club sites -- online or on a mobile device -- using the 2014 All-Star Game MLB.com Ballot Sponsored by Experian until Thursday, July 3, at 10:59 p.m. CT. The 2014 All-Star Game will be played at Target Field on Tuesday, July 15.
Fans may submit up to 25 online ballots, but they can also earn a one-time bonus of 10 additional online ballots. To access these additional online ballots, you must be logged into your MLB.com account when you submit any online ballot. If you do not have an MLB.com account, register on the site in accordance with the enrollment instructions for a free MLB.com account.
Fans this year once again can participate in the Home Run Derby Fan Poll. Fans will have the opportunity to select three players in each league who they would most like to see participate in the Home Run Derby. The 2014 Home Run Derby will be broadcast live on ESPN, ESPN HD, ESPN Deportes and ESPN Radio in the United States beginning at 7 p.m. CT on Monday, July 14.
The 2014 American League and National League All-Star teams will be unveiled on the 2014 MLB All-Star Game Selection Show during the weekend of July 5-6, with further details to follow on MLB.com. Immediately following the announcement of the AL and NL All-Star rosters, fans can begin voting to select the final player for each league's 34-man roster via the 2014 All-Star Game MLB.com Final Vote Sponsored by Experian. Fans will cast their votes from a list of five players from each league over the balloting period.
And the voting doesn't end there. The final phase of All-Star Game voting will again have fans participating in the voting for the Ted Williams All-Star Game Most Valuable Player Award presented by Chevrolet. During the Midsummer Classic, fans will vote exclusively online at MLB.com via the 2014 All-Star Game MLB.com MVP Vote Sponsored by Pepsi, and their voice will represent 20 percent of the overall vote that determines the recipient of the Arch Ward Trophy.
MLB.com will provide extensive online coverage of the All-Star Week festivities.
The 85th All-Star Game will be televised nationally by FOX, in Canada by Rogers Sportsnet and RDS, and worldwide by partners in more than 200 countries via MLB International's independent feed. ESPN Radio and ESPN Radio Deportes will provide national radio coverage of the All-Star Game. MLB Network and SiriusXM will also provide comprehensive All-Star Week coverage. For more information, please visit allstargame.com.